First of all, the major ones. The things that can, individually, stop me from buying a game, regardless of the game's merit.
1. Fixed controls. This is non-negotiable: you must let me remap my controls in every game and let me use arbitrary control devices. Computers have done this for like a decade, but consoles still aren't on board.
Yes, that means using a mouse and keyboard for a console FPS, and it had better not be gimped either, not even in multiplayer. I don't like gamepads for FPS games, never have despite trying them extensively, and probably never will. This can be a deal-killer for me.
2. Unfixable bad framerate - I find even the smallest disruption of framerate to be extremely jarring and to completely destroy my aim, so it is imperative that you avoid this. On the PC, you can spent more money or turn down the graphics, so it's not as big a deal. On the console, there is rarely any solution. I'd rather the game look like Quake than have serious framerate problems.
3. Don't transparently bilk me for money. Stuff like obviously overpriced memory cards or accessories, charging for content that should be free (bug fixes, stuff that was obviously intended to go in the original game), online services that don't provide servers (a lot of computer game publishers provide servers for free), and such. Even if the money you want is trivial, charging for it when you don't deserve it just angers me and makes me less likely to buy anything from you.
4. Bad hardware. I really hate dealing with returns, so the odds of me ever buying a Xbox 360 are not very high. Sorry guys, but I'm going to buy something I can reasonably expect to break soon. Consoles are not disposable.
Annoying trends that seem to be due to multiplatform games / console ports:
5. Punishing accuracy - Many games seem to think that accurate shooting at long range is to be avoided, or at least rationed, and provide the player with a sniper rifle that has approximately half a clip of ammunition in the entire game. For every other combat they're usually forced to rely on an assault rifle or SMG that has a ten foot spread when firing across a small room and was apparently made by airsoft. This virtually ensures that combat is changed from something challenging that rewards skill into an arbitrary trade of x health to pass y opponent, since you can neither kill them quickly nor from a distance.
6. Too much health, both you and the enemy - In many games, such as Fallout 3 and Bioshock, the amount of damage most targets take to go down is insane. Most monsters late in the game require an entire clip of assault rifle ammunition emptied continuously into their head to go down, and the player is rarely any less resilient (except on higher difficulty settings, in which case you die quickly, but the targets take even MORE damage to go down.) This makes the game unthreatening, and makes most enemies an obnoxious chore to kill unless you use the overpowered headshot gun. Which you never have enough ammo for (I'll make an exception for Bioshock, but any game that has you picking a crossbow over an assault rifle or shotgun for close-range combat has worse problems with its weapons.)
7. Audio instead of text. I don't want to spend five minutes listening to some flow-breaking audio diary, particularly if the voice actor sucks. I could read that much text in 30 seconds. I'm not illiterate, and I'm not on a low-res TV, so at least give me the option of reading a transcript.
8. Clipping issues. Clipping failure is jarring, it can unexpectedly block your shots, and it breaks immersion. Many of my attempted stealth kills in fallout 3 were stopped by some mysterious bullet-blocking empty space (but which still made enough noise when shot to alert the enemy.) And that's a game without severe clipping problems! I can only imagine the ones that actually get complained about in the reviews.
