There are a worryingly large amount, but I'll stick to my main bugbears:
Metal Gear Solid - Loved the first one on PS1, although I could never beat Liquid. I've tried to give 2 and 3 a chance, and I like the story enough to happily sit and watch while my brother plays them, but the actual gameplay is horrible. The last time I tried MGS3, I was playing 4or 45 minutes after which point I had watched a lot of cutscenes andsank into a swamp because I was aiming my gun at a crocodile and hadn't noticed I was sinking. Needless to say, I have zero interest in playing number 4.
Online FPS games - I'll happily play through the story mode of something like Reach on co-op with friends, but horde/deathmatch/ctf game modes leave me cold. You play the same couple of maps over and over again with no sense of progression except for your k/d ratio creeping up. I seriously don't understand the appeal (I have never played any COD apart from a bit of splitscreen zombies on World at War)
Red Dead Redemption. I could see the quality oozing out of it but I couldn't be bothered, frankly. I only played an hour or two, then never really wanted to pick it up again.
Also, for slightly different reasons, Assassins' Creed 2. I was really enjoying it, about 8 hours in. I booted up the xBox, went to my sae file and it wasn't there. I really don't want toplay the first few hours again, at least not while it's so fresh. I'll go back to it in a couple of months.