1: Unmappable buttons/keys:
I (and others) may like to remap their buttons/keys to where they like them. Maybe I want the game to have the same control scheme as "other, similar game" as I played that one first and like/am used to them? Maybe I don't want to use the LAlt key for anything as my fingers skipped a few yoga sessions and aren't quite that limber? Perhaps I don't like anything mapped to "mouse 3" as I don't like accidentally changing weapons when I reload one? It doesn't matter why I want to change them, just let me do it.
2: Rubberband AI:
If you can't code the AI to keep up with me then let them stay 15 seconds behind. Don't make them magically super fast with infinite grip only to make the race more interesting. Make the AI harder to make the race interesting or don't allow the player to overmatch the AI cars in said race with power/tire/weight restrictions. Cheating sucks, especially when the AI is basically hacking to beat you.
3: Horrible UI:
Bad menu design turns me off. If it takes more than 2, maybe 3 button presses to get down to business (read: start playing) then you failed. If it takes over 5 minutes to check the requirements for a level, go back and choose your loadout for it, then get back to the level to play it, wait for it to load, then choose start, wait for it to load then play... something is terribly wrong with your menus. GT5 I'm looking at you...
4: No V-sync:
I can get over the lack of anti aliasing in games these days. It's not supported in Unreal Engine and others and "jaggies" don't bother me much (except in pixel art/sprites, that's unacceptable) but screen tear? Gah! That's the stuff nightmares are made of (exaggeration). At least make V-sync an option... please. I payed for a decent graphics card and a pretty good PC to put it in, can I please get games that don't shred themselves when I turn around quickly?