FF13. The game was alright, but it didn't really click with me. I finished it because I vowed to play and beat every RPG I start. I no longer go by that rule. I dropped FF13-2 pretty fast and never looked back.
Several times. I want to be able to judge a game based on the entirety of the product and not just a portion. I want to be able to offer a meaningful review to friends who are considering it and not just say, "Oh, it was lame". I also sometimes can't help but wonder if a bad game may improve as I get further into it. There are lots of reasons really.
Plenty of time. The most recent was probably Resident Evil 6. Awful awful game but finished it just because I've finished every RE game I've ever played. Would have felt weird to stop in the middle of it but after finishing it I sorta wish I had. Just a total waste of time.
I used to make myself finish bad games like Final Fantasy games or Metal Gear games just because of hype. Tried way too hard to convince myself I was missing something about them but there came a point when I realized they were just overrated s*** and stopped buying into the hype.
If I've already invested a good amount of time into a game before I really realize how much I dislike it, I'd feel that time spent would have been wasted if I don't finish it. So I'll just go ahead and continue to the end.
It just annoys me to me leave something unfinished I guess.