BattleTech PowerHits collection and Legends of Terris
It was one (three) of the games that really got me into computer gaming and I followed that addiction with an online text based game that I would often dream about, in text. I still log into it every once in awhile.
Followed by Civ3 because it was a game I used to get my dad hooked on computer gaming. I'll never forget the Sunday morning we were supposed to go to a movie or something and I showed him my new game and we wasted the whole day on it without realizing it was already night time. Good times.
And last but not least HoMM2, sunk about a billion million trillion hours cubed on this and the sequel in both multiplayer and single player
Hmm, now that I think about it all these games, with the exception of BattleTech, I played with my dad so that seems to be a common factor here.