Most people have at least one game they got far in, but never/can't beat.
I guess I got a few.
Resident Evil 2: a recent one actually. I managed to beat Leon A, but am stuck in a tight spot in Claire B. I'll just have to move on to something else.
Ys Origin: Not a bad game, but very repetitive after having played Ys Oath in Felghana. Too linear, and the main character (Yunica) sucks. I'm halfway, so I could get back to it.
Far Cry 3: I wasn't too good, but long load times and bad framerate on 360 put me off moreso. I think I made at least 1/4 of the way through.
Legend of Starfy: Got this when I was younger. I was hyped, but the game was extremely easy and short. I could't beat the final boss though, since I couldn't tap the button fast enough.
I also couldn't beat Mario & Luigi: Bowser's Inside Story for the exact same reason, until I replayed it a few years later.