Teh Win. Also has excellent title music - the song on the menu screen is entitled "Baba Yetu", and is the Lord's Prayer sung in Swahili. It is one of the most amazing pieces of music I've ever heard. It's also horribly, horribly out of place in this game, if you know what it means. I find myself humming this song at work, and not being upset that I'm doing that.
It's the game you know and love, but significantly changed. Corruption is gone, pollution is (mostly) gone, the mandatory city size limits have been removed, and infinite city sprawl is a thing of the past. Spearmen can still win against tanks every once in a blue moon, though. :)
There are a TON of map types, and the AI actually shows glimmers of intelligence in their movements - if you hole up in cities with strong defensive units, they'll pillage the countryside. If you venture out to smack them, they'll try and raze cities they can't hold, and capture cities they can. Diplomacy works really well - you treat a civ nice, and it will actually keep an alliance with you, assuming you're not a pushover. If you are a pushover, or the civ is militaristic and it feels like it, they'll often try to roll you even if you are a friend.
Kinda like you would if you were on the other end. :D
There are two significant departures from the original game, besides the new 3d engine:
1. Civilizations each get traits based on the leader that affect how that civilization plays.
2. When producing settlers and workers, you don't lose population when completing the unit; instead your food is added to your production to determine the total number of hammers, and your city no longer grows in size.
Hell, there's a lot more than that in the game, but it's all very well thought out, and it works great.
Edit: Forgot to mention the graphics. Bloody amazing looking, each city has every single building out there in the open on the world map. Looks absolutely beaut.
I love this game. ****. Would buy from Sid Meier again.