Games with poor controls are always a repellant for me, along with an unreasonable difficulty curve. I hardly ever finish games though (I just can't stick to one game long enough!), so if I suddenly get stuck on one point for a while I tend to lose interest fast. Not to say difficulty is BAD. If I know what to do, but it's difficult TO do it, that's a fun challenge, but standing around thinking "what now?" for an hour is not fun. At all. Even if it has nice graphics to look at.
I've also got an interest in plot and characters, if they're the same old "wit"-spewing cliches, I just cringe at the game and have to turn it off to save it embarassing itself. Also, overly-"realistic" graphics, ie, you'd see brown if the lighting wasn't so pathetic. Honestly, I prefer bright grames with shiny eye-candy graphics as opposed to a big brown-o-fest with a hint of grey for variety.
I recently got Fallout 3 and I loved it from the moment I started walking around the Vault smashing in the heads of my fellow Vault-dwellers... but once I reached the first town it was so frustratingly dark I'd often myself stuck walking on the spot and not even noticing that I wasn't going anywhere. I've always meant to start playing it again because the outside world looked really interesting but the lighting was just so... off-putting.
P.S. I'm not saying Fallout 3 is a bad game because I must have played a total of 40 minutes of it and can't judge. From what I've heard, it's a great game and I'd love to play it but the world they live in doesn't appear to have a sun.
EDIT: And, obviously, as the people above me reminded me, if I'm not actually having fun then the game can't be that good.
