Yeah I was going to mention Disgaea. I've actually kind of avoided those games because I know I'll end up slaving away at them. However, stuck in space with little to nothing else to do, I'd be fine throwing significant hours into one of them.
I can think of a few more that I'd be fine with. Diablo 2, even Diablo 3 on console. I put 700+ hours into D3 on the pc alone and countless more into D2. Diablo 3 gets a lot of hate, but I enjoyed my time with it immensely.
Any major Bethesda title would work. There's just so much to do in those games.
Final option would be some technical 2d fighter, something you could really spend some hours on honing your skills. BlazBlue, Guilty Gear, KoF, something like that.
What? Dude, you can't ask a question like that and expect me to supply a single, straight answer. I could never choose one, just let the random crash decide which game I play for the next 3 years.