I still play Civ2 even though I have the newer Sid Meier games (Alpha Centauri and Civ3). In my opinion, it's the best one of the series, simply because it gets the perfect balance between complexity of the game and playability.
The concept is the same as Civ 1, as a matter of fact very little changed between 1 and 2, except that the graphics are vastly improved and some new technologies (and therefore buildings/units/wonders) have been added.
The replay value of the game is exceptionally high, as indicated by the fact that I'm still playing!