Re: Games started but never beaten.
Counting every NES game I've popped in from time to time, there's a bunch. Games that I've actually made an effort to beat though, well...
Medal of Honor: European Assault. I think that's the name of it anyway. The last level is a pain, it takes about an hour of relatively easy crap to get to the final battle and then I just loose all my lives. You're timed to stop a bomb from going off and the nazi guy is firing a machine gun at you from the top of a bunker with guys coming down the side non-stop. I never have a chance to figure out what exactly to do since I can't seem to kill him from where I am and you have no time to explore or try new ways to get around. And since every time I fail I have to play through another hour I've just said fuck it.
Battlefield 3 - Single player was dull and I just got bored and turned it off. Might go back sometime.
Pokemon Conquest - Same deal here, I got bored and haven't touched it since.
FFX - I was stuck at some part where you have to kill a dragon boss, fight your way through some tough guards, and fight an even tougher boss all without checkpoints. Anyway I let my friend borrow the game and never saw it again.
Need For Speed: Most Wanted - The original version not the new one. Again I was stuck, haven't played that one in years though.