Some people seem to be bewildered by my choices, so I'll explain a few of them.
Silent Hill 2 (PS2)
I heard it was good and I wanted to give the survival horror genre a try, but after playing for a few hours I found the entire concept of survival horror to be extremely stupid. Solving simple puzzles that are stretched out with backtracking while avoiding enemies is not fun to me. Making combat purposely slow and difficult just seems stupid. I don't understand how the entire genre is supposed to be fun. That doesn't mean the game is bad, but for me at least, this game is completely unplayable.
Yu-Gi-Oh! The Eternal Duelist Soul (GBA)
I get irritated that no matter how well I do, there's always a chance that bad luck will suddenly cause me to lose. Combine that with that fact that the gameplay almost never changes in the least, and there's not incentive to continue. "Hooray, you won a battle! Now you get to do the same exact thing you were doing when you first began this game!"
Spyro: Year of the Dragon (PS1)
I loved playing this game, I just have no desire to finish it. I included it because this thread is about games "you never care if you see the ending". To get to the final boss, you have to collect a lot of something (I forgot what) that you never had a reason to collect before in the game. So suddenly at the end I found that I was going to have to go back and replay through levels searching and searching to find what I needed. That didn't really seem like much fun to me, and since the endings of Spyro games never seemed that great, I didn't really care if I finished it or not. No matter how many times I play that game, I doubt I'll ever finish it. The game was fun, but the extra work required for the ending doesn't seem worth it.
Kirby's Tilt 'n' Tumble (GBC)
Whenever I play this game, all I end up doing is fighting against the terrible controls. If it wasn't for the badly-implemented tilting you had to do, the game would have been very easy and I could have beaten it with no problem. I've never found fighting against bad controls to be fun, and I'm having the same problem with the terrible combat in Prince of Persia: The Sands of Time right now, which I currently hate.
There have been lots of games I hate that I still finished due to cheating to get through with them quickly, such as Digimon World, Dark Cloud, and Dr. Muto. But my Gameshark won't work for Spyro:YotD or Silent Hill 2 for some reason, and I don't have a cheat device for my Gameboy.