Master of Magic
Master of Orion II
I chose these simply on how much time I spent playing and the replayability of these games. I have only ever played two RPGs more than once, which was fall out 3 las vegas and vampire:bloodlines. However I played bloodlines through with each clan at least once and some of them twice.
Civ IV was just the best of the series. Mechanics, map generation, balance, etc. Civ V has better graphics, but that's simply due to advancement in real world technology.
No one has come close to Master of magic. I'm hoping E:FE will be close, but i doubt it.
Same as for MoM is MoO II.
Madden 07(on the PC) My guess is most poeple would say you need to have some interest in American football to enjoy, but I disagree. The ability to draft new players year after year, the variety of plays you can call, the way the players graphically respond to things on the field, the coaching/player stats you have to pay attention to, subbing players, making your own plays etc etc. Its simply a well done game with tons of replayability and things to do.