1.Reloading is easily interrupted by sprinting, necessary?
2.Recoil for some weapons is extreme, it sometimes puts the sights way below the original aimpoint (pistols) after the first shot.
3.Blinding effects. There is just too much going on in confined spaces at times that makes it hard to realize where the damage came from.
4.The lack of chat (voice not recommended on mixed language regions anyway (EU)). The game is enjoyable when you bring friends you already know from other games. Solving puzzles with randoms is a pain in the nether regions. I know about the legal issues in America, stand up against that sh.. already. All American game devs should unite and make a motion or something. It really hurts future games. Since it is an American law, can't you offer an external (3rd Party) chat overlay that is situated in Europe and circumvent the problem that way? Even in voice it is hard organizing stuff when too many people talk, especially in large guilds.