Sid Meiers Civilization Series
Civ IV BTS is the best
I liked it. However, all "building" games have the disadvantage of being complex enough you have to relearn them if you haven't played for a while.
I'm a huge fan of the series. I was a little disappointed that they didn't address some of the problems with Civ 5 in the new one though.
The ads look cool.
I was thinking about asking this yesterday, as I opened the game. I installed Civilization (the first one) as a lark on my son's computer not too long ago. *sigh* #nostalgia