Lag, bad spawns, bad voice acting etc.
And in multiplayer: The people playing it! Seriously, there are so many ******s out there playing like retards. Annoying as hell

Lag, simple as that

Glitches and noobs on multiplayer games.

bosses that you think are the final one,but another one just appears out of nowhere

Lagg is not really a problem for me since I don't really play mainstream videogames, or when I do it is after another one already came out so the multiplayer isn't overloaded. I don't really mind glitches since they are quite fun to try to find nd sometimes they can be really cool like I remember one glitch which adds a whole other part to the map if you use the glitch.

Two things I don't like is when a videogame dosen't bring anything new and just takes everyone elses ideas to try to make it big, and I hate when there is unfinished rooms. If you ever fully explored arcadia in Bioshock then you know what I'm talkig about, it is rooms where developers thought that no one would go to and once you do since developers thought no one could go there, there is no exit... which completly ruins your save and progress. I have had that about 3 times, but it is ALWAYS when I am almost done with a level.

Fallout pisses me off. I mean, I love the game and all, it's epic. But it's soooo annnoying when you've got loads of quests still going on, you're not even a very high level and you've done barely anything and you decide to do a few quests in the too-short main story, and poof, the game ends.

Firstly, make it more challenging or something. And also make it like TES games, where you can carry on after the main story.

I also hate bad voice acting, as somebody said earlier.

Also, on CoD when you die from like, one bullet but on the killcam the enemy seems to shoot you for far too long, with absolutely no recoil on a gun with too much of it when you use it.

Finally, on games like Red Dead Redemption, don't get me wrong, epic game, but when you get hit with slight power or fall down a small hill, you end up on the floor holding your head for 999999999 hours and end up getting killed.

Lag, noobs (especially when they're on my team), hackers, glitches, bad voice acting, awkward controls, bad graphics (but I like the retro graphics like from PS1, N64 and SNES), impossibly difficult levels/missions/objectives/quests, and repetitiveness. Yup. If a game has any of those, I probably hate it.

Lag,

Lag, simple as that

LAG ! That's it >:-/

You all just suck.

Personally, I hate it when there is a set camera angle that you can't change. This is even more horrible on platforming levels.

Lag, noobs (especially when they're on my team), hackers, glitches

That's not really what you don't like about the game, it's more what you don't like about people playing the game. You really can't blame the game for the public that plays the game, it's not really their fault (except cod doing lag compensation, let the bad pingers suffer and not bring everyone down with them)

bad voice acting, awkward controls, bad graphics

I used to agree with that until I started playing indie games and then I relized how hard it is or expensive it is to get good voice acting or graphics, I really don't mind that people didn't spend two hours designing a flower pot of a peice of grass, but it does look funny when developers cut corners and don't detail parts of a monster or something because in the game it is constantly moving, but when looking at a still version of the model you can see the obvious blurs.

repetitiveness

You pretty much just ruled out every single rpg game because that catagory almost always goes with monster grinding.

impossibly difficult levels/missions/objectives/quests

When the game is set to impossible, I usualy don't blame the game for being impossible, and if it's impossible even on easy mode, either you are not used to playing it or the person who made the game was evil and wants you to lose.

What I hate in a game?
I would say games that require perfect timing or close to it and games that have repeated elements in a game with no actual addicting action.