Civilization’s 1 and 2 were perfect games for me. I spent hundreds of hours building empires and crushing my neighbours beneath the tracks of my tanks. The later versions added concepts I loved but the endgame became tedious. I haven’t played versions 5 and 6.
In this GDC talk Sid Meier and Bruce Shelley go fairly deep into the design, programming of the first Civilization, talking about the constraints and design philosophy that made the game a hit and set the series up for success.