Civ 5 if your into that kind of thing. Long lasting and always different depending on the path you take.
Stay with the original and get Civ NiGHTS. GREAT mod.
The expansion was pretty 'meh' and the latest patch made it a joke. The other night I focused hardcore on science and science alone. I had 4 cities around turn 120. Each AI civ had at least 8 and around turns 140-160 they started getting crazy gains in research and wonder production. IDK what the problem is but tons of people are bitching about it.
ETA: CivFanatics Forum
That place has some great tips.
This post was edited on 12/3 at 11:52 am