I know for me, too many games are "of their time". I've spent more time playing the Ultima games than all other games combined, and it's not even close. Given what I know about games today, I'd be hard pressed to go back to, say, Ultima V and play that again. It's not a game you can just dip your toe into for an hour or so, and the effort to put in doesn't really do justice to the legacy. I'm not 22, single, sitting in my bedroom pulling an all-nighter playing Ultima V, eating pizza and listening to King Crimson.
Others, like the first Black Ops (Call of Duty), I can go online, join a game and have a reasonable amount of fun. Or I can play the two good Rainbow Six games and have some fun.
EDIT: For this reason, I'm holding off on the System Shock reissues available on GoG. I want to play them SO BAD, but I downloaded Dark Forces (I think it was on Xbox) and it was almost unplayable, and it bummed me out a LOT.