Problem: in most kinds of D&D, the cooler the stunt you made up, the less practical it is to try to do it.
At least playing by the book.
"I want to cut the chain in mid-air so the morningstar ball goes flying"
"Ok, that's minus 2 for a called shot..ok, roll..."
Naturally if you roll a natural 20 you do whatever awesome extra cool thing you were thinking you'd do, so...
Here's the deal: if you want to do something real specific--like hit the orc's torch and knock it on the floor, you can if you roll a crit. You can also extend your crit range as much as your heart desires: natural 19-20, 18-20, 16-20, all the way up to 11-20. Your choice.
The only catch is you then have to extend your fumble range from one by the same amount.
So you really want to knock the Necronomicon out of the cultist's hand? No problem, you want it on a 15-20? Ok. But on a 1-6 you trip and accidentally stab the baby he was about to sacrifice. Or yourself. Or your dad. Or whatever your DM's cruel little heart devises.