Around 1977 or so on a huge basement-sized mainframe with some computer science major buddies. A great way to waste time and build up some nerdly coolness points. "Beg your pardon, captain?" Shortly afterward some of the predecessors of Zork, Colossal Cave, was it?
Later, Parsec on a TI 99/4a used up a lot of my time. The first few King's Quest games. Lot's of computer and console games since. I'm having to compete for time on Super Mario Galaxy now with my kid. My son's friends (or my wife, either) can't believe that I like to play games now so much, though the real pleasure still is in the puzzle solving.