Get Valkyrie Profile: Lenneth. If you never played the original on the PSone, you owe it to yourself to play the port. They re-did the cutscenes, but otherwise the game is pretty much untouched. You can easily spend 40 hours on normal mode if you make sure to use all you time wisely.

Or get Lumines. There's no campaign mode or anything, but you quickly become addicted and play for long periods of time. I've had the game since its release and still pull it out to play it sometimes.