Forced tutorials annoy the shit out of me. Even if I've played hundreds of hours of other games with similar mechanics, and even if I've beaten that very game several times, I STILL have to sit through a boring few minutes as the game tells me what a controller looks like. That's why tutorials should be integrated (don't know what I mean? Look at Mass Effect 2's first level--it's a combat tutorial that takes place as part of the actual game) if they even need to exist in the first place. Also, if you're going to have a tutorial like the one in, say, Modern Warfare 2--everyone's favorite punching bag--make it optional. It gets really old to be taught how to play a game that you've been playing for years.
Also, people bitching in multiplayer. If you don't like someone's tactics, DEAL WITH IT. I don't like campers, but if I get camped, I just remember where they are and come up with a way to deal with them. Next time, don't whine about how unfair something is, retake the advantage (after all, campers don't move very much... they're not hard to sneak up on if you're smart about it).
Thirdly, 12 year olds with microphones. This is pretty self explanatory.
Finally, NPC allies. I can't even tell you how many times I was sneaking up into perfect ambush position when my allies decided to go Rambo on the enemies, leaving me out of cover, in plain sight, and with several new holes in my body. Besides, they don't usually do anything other than take a few shots to the face and then die--but strangely, they always seem to be more resilient than the player character (have you ever noticed how you'll go down in a shot or two, but your allies can often take half a magazine of assault rifle fire before they go down?).
I could probably go on (enemies that never need to reload, too few checkpoints, unpolished games, unbalanced gameplay, etc.), but I think that this covers the highlights of my gripes. Sorry about the minor ranting.
