I like Civ4. It's as addictive as always, but more fun this time round - especially the Great People and the combat system (combined arms+promotions).

What I like best about it is that Civ in general is that it provides a competitive challenge from the AI that virtually no other strategy game does (certainly not TW, unfortunately) and yet diplomacy is still meaningful, with some scarey civs being a threat and others being nice to you.

I'm not sure about the expansion. I've never played Civ scenarios - they seem to want to turn Civ into a historical game and I just can't accept it from that point of view. The changes to the core game sound rather peripheral.