Always go back. Divine Divinity, Diablo 2, Baldur's Gate, Planescape: Torment, Titan Quest, A Farewell to Dragons, Planet Alcatraz. These and others stay installed and get a few hours each here and there in between the big releases as the years go by.
Always looking for the best/most fun of them all. Any suggestions of great ones to try? List your favorites and ones on the horizon that we can look forward to.
...Umbra looks like it will be pretty badass...if it ever comes out