The board's died down since Resonance's release and I thought to try to liven it up a bit.

I didn't know what to call this, so I called it a "forever" game.
It's a game you always go back to, and possibly play into the early hours because you lose track of time.
It's a game you go back to after playing and finishing some new games you got. Even when the new games have replay value, and you replay them, this game is sitting on your shelf, most likely still installed on your computer, waiting for you to come back to it.
It's a game that you don't know where a good save point is, just like a good book.
It will always be your favorite game of all time.
Yes, I might be weird, but who isn't.

For me, my forever game is The Sims. It's a game I got hooked on back in 2000, shortly after it's first release. It's the first game I install on a new computer, and I have multiple backups, even though it's fun to start over.
Do you have a Forever game and what is it?