Forgive me if I ramble a bit, this is just a thought that occured to me and it is probably not fully fleshed out at the moment.
I was just thinking on FPS games and it occurs to me one of the areas where they DESPERATELY need to improve, specifically in the fields of hit detection and damage management. Allow me to ellaborate, you know how in FPS games you can pretty much aim anywhere at an opponent's model and kill them with enough shots that connect? Pretty much every FPS game nowadays balances hits vs damage irregardless of where that hit is. So you will score a kill to your enemy just as surely if you hit them in the heart or blow off their shins. The only exception to this rule is the head, you hit an enemy with anything stronger than a wad of wet paper to their fragile little cranium and they're gone.
This lack of differentation seems to be a major problem to games in my eyes; just imagine if modern FPS games could tell the difference between shooting your opponents in a limb or shooting them square in the heart. Think of the deeper levels of gameplay that could be implemented: you could take out your opponents' legs, trapping them in a crawling stance; you could disarm enemies, forcing them to switch to a weaker weapon or run off in hopes of reclaiming their lost one.
What's funny is I've seen similar elements used in other games, it's not like the technology is beyond the developers' reach. If they just put forth a little effort rather than rehashing the same old bullet sponge methodology, they might actually push the genre forward and create some truly remarkable games.