I was thinking there should be a robots-in-the-city game that does for underground hip hop and electronica what Vampire: TM did for goths. I haven't written or more importantly drawn it but it did get me (and False Patrick) thinking about robot games.
After thinking about it way too much, basically I decided the one thing robot games need to have that others don't is hit locations.
Here's some work toward that:
Each body part has an armor die: d4, d6, d8, d10, d12 or d20. Beginning PCs will probably have a d4 in most everything and maybe a d6 or two.
Every weapon has a damage die: d4, d6, d8, d10, d12 or d20.
Body parts used as weapons (punches, kicks, headbutts) generally inflict damage equal to their armor rating. So if your arm is armored up to d8, it does d8 damage when you punch people.
Combat works like this:
Attacker rolls the damage die of the weapon you're using and chooses a body part to attack.
Defender rolls the die of the armor for the body part being attacked.
If the defender rolls high: no damage.
Attacker rolls high, it inflict a number of criticals on that body part equal to the disparity in the dice.
This then requires cool d100 critical charts for each body part, but that's the basic idea.
Also probably want to work in a mechanic where if you give up your attack for the round (or maybe accept a penalty) you can first roll an Agility Die (likewise rated from d4 to d20) to avoid the blow. Beating the opponent by a little means you shift the attack to another limb (or a shield) beating them by a lot means you dodge altogether.
This means the defender is often rolling as much or more than the attacker, which actually seems appropriate for mech combat.