Civilisation, the original one. Got it in the 90s, and none of my computers was without it. Even now I sometimes launch it for a guick, half-day game.

I’m sure other Microprose games from that era, in particular UFO: Enemy Unknown, are on my top 10 most played games.

From modern games, I probably spent the most time playing Civ4 and Heroes of Might and Magic 3.