Developers who won't fix glitches.
Lack of freedom (GO HERE, GO THERE, stuff like that).
Hackers.
Snipers.
Idiots who bug you for liking a certain thing about the game.
Lack of an interesting story.
Lack of an interesting ending.
No side things.
Incredibly fast gameplay (So you don't know what's going on half the time).
Snipers.
Games that reward you for doing better then the enemy, meaning if you're the one doing bad, you're screwed.
Instant failure for the smallest mistakes.
Overpowered stuff.
Snipers.
Smoke grenades.
No way to get more ammo.
Horrible platform placement.
Puzzles that make my brain die.
Snipers.
And Snipers.
EDIT: I almost forgot, Snipers.