The Last Remnant. I have 95 hours recorded in that game and it's an embarrassment every time I see it on my Steam profile.
Basically, being primarily a PC guy, but having played a few PS1/PS2 JRPGs when younger, I decided to buy the game to essentially support more Japanese games being brought to PC - since other than the old (bad) ports for FF7 and FF8, we weren't really seeing Japanese games coming to PC at the point in time that TLR came out.
I put around 20 hours into it that I enjoyed well enough, but started to get tired of it at that point. I should have just stopped playing, but having already "invested" 20 hours in the game and with a tinge of OCD coming into play, I felt it would be a waste not to finish it. Well, damn my psychology, because I had no idea it would take another 75 hours to get to the end.
I had to actively force myself to finish it and it was a huge relief when I finally did (and only with the help of cheats, because despite putting that much time in the game, I still couldn't beat the end boss). What's "funny" is that despite having spent that much time with the game, I honestly remember nothing about it. You could show me an unlabeled screenshot for the game and I wouldn't be able to identify it as belonging to The Last Remnant versus any generic "Asian styled" MMO or RPG unless I recently looked at other known screenshots for it.
I wish I could break myself of the "need" to finish games, but I've since repeated the same pattern with The Witcher 1 (in which I should have just stuck to the main quest), Final Fantasy 13, and Amalur as several others have mentioned. None of those was as bad The Last Remnant, but I still had to push myself to finish them after tedium set in past the 20-30 hour mark.