Civ 5 is still largely considered a joke compared to the rest of the series. I played it for a few hours and was disgusted at how painfully simple it was, with the facade of depth, and some absolutely bone-headed AI.
Hopefully some of the patches have helped with the AI, but Civ IV is still a vastly better, deeper, more strategic game.
Eh, it was great fun IMO. I never cared for the fiddly numbers game anyway.