5th edition D&D's skill list has always struck me as a pretty good list of the kinds of things characters try to do outside of combat, but a lot of old schoolers glaze over at any kind of skill-based system and I'm not sure I blame them. When I switch to AD&D from 5e I barely notice any layer of depth missing.
So: how do 5e skills compare to how the same activities would be handled in an old school game?
Perception--Oh boy--first one's the hardest. This is a case of old school being more micromanaged than the current edition. There's Hear Noise which just covers thieves saying "Hey I'm gonna stop and listen carefully", Find/Remove Traps and several different (usually racial) abilities to notice specific things like dwarves have a chance to notice odd stonework in certain editions, etc and then LotFP's Search which is the Specialist (Thief's) active "Look around" ability. There may also be buried away in the originally Unearthed Arcana or 2e some stuff about druids or rangers or barbarians noticing specific stuff but checking would require getting out of bed, which I refuse to do right now.
Popular semi- and unofficial ways old school would handle other aspects of this are:
-The classic "careful examination" which means the player describes that they look at it or turn it over or whatever (some modules include a time limit like "If examined for at least 3 minutes you notice there's a Potion of Gaseous Form hidden in the carpet").
-Wisdom check as a passive perception check
-Some modules would point out special noticeables by being like "A magic-user will immediately notice an eldritch energy in the air". Which gets into the thorny thing about how basically every knowledge or lore skill could be lowkey considered a perception skill if you think about it. (PS in Call of Cthulhu like half the things on that sheet are kinds of perception skills, and in Night's Black Agents even more.)
So what's better? One explicit reason for Perception being a skill in 5e was so that rogues/thieves could have better chances of noticing stuff than clerics. That makes more sense to me than the straight Wisdom check at least in dungeons (clerics are only wise in a non-niche non-technical environment). The hodge-podge of "notices" is just that: a hodge podge, and are hard to DM in a passive situation because you're like "Uh...who has a bonus to sense sloping corridors? No reason..." which leads to these only being used actively.
In practice, I tend to use a passive perception check a lot because:
-I want to convey the layers of information between "It's a stone room" and "Oh, you look at the chandelier? Well you see..." Often this is useless information on purpose that just is some setting stuff because I want to cram in as much detail as possible ("The architecture appears to the paladin to be Late-Decadent-Albino-Dogman").
-If you're doing like overland travel for hours it isn't practical or nice to be a straw old school hardass and go "Aaaand what are you doing the next minute?" for every minute of a journey, but at the same time you want to be able to ambush-murder players while still giving them a chance of a subtle clue first. Passive perception is good for that.
...so having that as an official thing is good. Getting rid of thief Hear Noise doesn't really lose you much, but I like the race and class-based ones, like dwarves notice stonework, elves hear stuff because pointy ears, etc. it's probably easy to be like "Ok, Plover gets advantage to this one"--which does take some effort on the part of the GM but no more than remembering Halfling's get a 2 in 6 to notice pie or whatever so I'm gonna say 5e gets it right on this one.
Athletics--Strength-based feats of physical prowess. In games like Runequest and 3e this would break down into like Swimming and Jumping but at that point it's a detail fetish--this is mostly just stuff old school would handle as a strength check and I'm good with that.
The only reason it's a skill in 5e is technical: so that strength-centric classes get the proficiency bonus to doing strengthy stuff and so are as good at those things as other classes are at their things--ie so that when the druid is extra-wise when looking at a tree, the barbarian is using the same probability math when trying to arm-wrestle.
In other games being good at sports and being strong might be worth hair-splitting about, but in D&D you can be pretty sure that's basically why they took you along.
This skill is a strange outcome of trying to do everything on the same die and on the same scale--skill checks (modifier plus skill bonus, which goes up as you increase in level) typically involve bigger numbers than ability checks (modifier only, which only goes up when the whole ability score goes up--which is often enough in 5e), so for simplicity's sake it's a way to make ability checks into skill checks. In practice it kinda doesn't matter though--see Persuasion/Deception below for an example of how this plays out.
Handling some stuff with broad ability checks and some stuff with training-oriented skill checks (with better math) is only hard once you got a bajillion skills because then the DM has to remember what all the skills are. This is a problem in like Chill 2e. In D&D there's not so many skills so I don't see why they tried to make all the math the same.
The only exception to the pointlessness of Athletics is climbing: Goats, monkeys and thief-types are supposed to be able to climb stuff without being very strong (this is a major point of skill systems: to have people be good at specific parts of things they aren't broadly good at. Like you need to be able to make an idiot who knows a lot of Dr Who trivia.) Old School handles this as its own (usually thief) skill, which makes sense in the more archetypal world of those games, but it works in 5e if you always handle climbing under...
Acrobatics--Agility-based feats of physical prowess. Old school games would handle this with a dex check and--again--it's basically just here to give Dex-centric classes a proficiency bonus to the kinds of things their class does. Outside that technical reason, the only good reason for Acrobatics is it's a place to put climbing (dodging is handled with saving throws).
Sleight of Hand--Gary thought it mattered a lot that while you had a 3 in 10 chance of Picking Pockets, you only had a 2.5 in 10 chance of Opening Locks and a 2 in 10 chance of Removing Traps but he was the only person in RPGs ever to think that. As a long-time AD&D thief player I can definitively say the father of role-playing games was full of shit wrong because what you really have until like 7th level is a really good chance of dying if you try any of those things and many retroclones agree--Lotfp bundles these skills as Delicate Tasks or whatnot. Old School and 5e are almost identical on this score.
This also points to the other reason for skill systems at least in D&D--creating things that only well-trained people can do, but that also (unlike ability checks) you get better at as you level.
Stealth--The Artist Formerly Known As Move Silently and Hide In Shadows and another fine example of pointless Gygaxian 5% difference hairsplitting and another example where LotFP uses the same skill--this time calling it the same name--Stealth.
Arcana--This is the wizard's equivalent of Athletics--the skill they get to represent their smartness is especially wizardy smartness and just balances out the math so they are as good at their thing as the thief is at theirs. (Obviously skills like this also let you build PCs with off-class skillsets like a scholarly thief, an undeniable perk of newer games if you are into that.) In old school you'd just have this be an Int check only wizard-types could do, which....works fine.
History--Old school doesn't have this and as a guy who has literally hundreds of pages of stuff he wrote about his stupid D&D world I like it. It's a nice way to throw useful info and red herrings at my players. Can't think of a lot of reasons for it not to be something any character with a high Int could do, though.
LotFP has Architecture, which overlaps with this but is less useful if you're looking at a chalice and more useful if you're looking for hidden rooms, but then that pokes in on Search.
Some old modules handle this kind of thing as "PCs from Greendale have a chance to notice that..." which is pretty easy to implement.
Investigate--I hate this skill. 90% of the uses for it overlap with stuff I want to rig so the players can try to figure it out themselves ("The corpse looks like it was killed from behind by a bunch of needles and there's some pinholes in the wall, so..."). I have to work to find ways to not cheat players who got proficiency in this out of their 2 points worth of D&D and probably so does every other old-school-minded GM.
Arguably it is also trying to be for Intelligence what Athletics is for strength--the skill that balances out the math. It can fuck right off.
Nature--What rangers and druids have in common (and some barbarians). This is a good new skill because it covers things those classes should be able to do at a level better than someone else of equivalent Int. In Old School systems which have rangers and druids this is broken down into stuff like Identify Plants and whatnot which so far as I can see confers no important playable benefit. Good job 5e.
Religion--Looks at first like a math-balancing cleric equivalent of Athletics (for fighters) and Arcana (for wizards) but it isn't for two reasons.
First: a lot of the time this applies to other peoples' religions, like Iceblood Orcs of the Fuckwastes. So this is not just about how to be a priest but identifying a broad swath of the culture going on in your gameworld (presumably because it's heretical and needs to be annihilated).
Second: it's Intelligence-based and clerics are supposed to be good at Wisdom, so the idea here is that knowledge of scripture and holy lore (especially other peoples') are secondary skills for a cleric, which makes sense. A D&D cleric is not necessarily so much a scholar as an armed zealot.
Old school would typically handle this with an int check that only clerics could do, which loses a shade of subtlety, but maybe not enough to matter.
Animal handling--Arguably part of druid and ranger (and for horses, paladin) skillsets in AD&D 1e but basically new. This is my favorite 5e skill: it's something that comes up a lot (in and out of combat), it defines a medieval world, it makes sense for a variety of classes to have it (it's one of the fighter options because: horses and guard dogs), and ladies love it.
Insight--Telling if people are lying, mostly--plus other interpersonal details the GM might not want to trust to his or her acting ability. The most proximate ancestor is Call of Cthulhu's Psychology skill but old school you could handle this with a Wisdom check, and Wisdom without this is barely Wisdom.
Medicine--An odd one. Somebody smart pointed out that there are very few uses for this skill, rules-as-written. Old school has no skill here, although various Death and Dismemberment tables allow an Int check to help an injured PC in some cases. I put it on my 5e one to give it some more use.
But in the end, even if you rewrite the rule so magic healing doesn't do all it could do and more--do you need a niche for someone who is better at medicine than they are at general Int-oriented tasks? Might be a pointless skill.
Survival--The other thing rangers and druids (and some barbarians) are supposed to be good at, and which AD&D handles kind of scattershot in the abilities for those classes. It makes sense to bundle hunting, tracking, fishing, etc in one skill and it makes sense that a ranger can be wiser when hunting than they are about offering advice. I also like the idea that a druid who takes this skill is typically better at it than a ranger of the same level (better wisdom) because they just like disappear at camp-setting-up time and come back with a pile of dead warthogs like what?
This plus Nature would be identical to the LotFP specialist's Bushcraft though serving a slightly different purpose since there are no rangers or druids in that game. Ok.
Performance--Old school would handle this as a dex or charisma check (could also see an argument for sleight of hand). It could be argued that if you do that you lose the ability to differentiate a trained musician from a gymnast holding a mandolin but I can't think of any reason any sane person would care in a D&D game. PS still fuck bards.
Intimidation--Surprisingly useful in that it often does what a reaction check does in old school. It is a little weird though because intimidation capacity seems more a function of charisma plus how big, scary or well-armed you look rather than charisma plus a special skill plus level. It's not a skill in old school, but would be derived on a case-by-case basis from those factors. And if it's a matter of looking more dangerous than you are then that seems like a species of Deception?
But then again there's that issue of Daredevil where DD is missing and the Human Torch (who can set things on fire by looking at them) has to take his place as urban vigilante and sucks at it because none of the lowlifes or hoods believe he'll light them up. So maybe Intimidation needs to be a skill. Convince me?
Persuasion--This is just straight up a skill that exists so charisma checks can use the same math as strength checks boosted by athletics etc. Old school would just use charisma. However...
Deception--Well there's charisma as clerics use it and charisma as thieves use it. Fair enough. Old school does not make this distinction at all, though it is meaningful.
Here's a weird result: if they didn't include Persuasion as a skill and just relied on Charisma, yet Deception was a skill, then that would mean that after a few levels you would always be better off lying to someone than telling the truth. At least in the abstract--realistically the GM would/should simply set the DC of convincing someone by lying higher than by telling the truth.
So altogether we've got:
1. Reorganized thief/rogue/specialist skills (Acrobatics, Sleight of Hand, Stealth)--these are by most measures just more useful than their old school counterparts and there are less of them, so definitely a vote here for 5e solely on the grounds of simplifying life.
2. Reorganized ranger/druid/maybe barbarian skills (Nature, Survival)--as thief skills, these are a clear improvement because they're simpler than their old versions without losing depth.
3. Skills made necessary by the system math (Athletics, Arcana, Persuasion, Insight) You're not missing much by excluding these from old school play, except the ability to make your PC less archetypal on paper (cleric who is a witch hunter so knows a thing or two about Arcana, for instance)--but you knew that when you decided to roll old school.
4. Borderline, arguably useful depending on the campaign/rulings but could probably be absorbed into parent ability with no big loss (Performance could be assigned to dex or charisma the few times it comes up in a properly bardless campaign, Medicine, History and Religion can be Int).
5. Total abomination (Investigation)
6. Oddball thing I'm not sure should work like other skills do (Intimidation)
7. Genuinely clarifying or adding new level of detail to the game (Animal Handling, Deception, Perception)
My overall verdict is no matter how you slice it, old school games have some weird problems around noticing shit and 5e has players making a few more choices during character creation than they probably need to.
Happy New Year!