You can't stop playing! Excellent game! Best of civilization series game, highly addictive.
Graphics are outstanding, all playable scenarios are an unique experience, i'd recommend the Mediterran Sea campagin and the American Revolution one.
Negative aspects? Well, this game lacks something that was a classic on other civs games: The Palace or Throne Room (depending on which civ game u're talking about), i miss the "you citzens are happy, they want to improve your palace"...
Game is better balanced, Nuke won't give you god-like powers like other civs games, barbarians are now "intelligent", not a bunch or city raiders, they build towns, steal your workers, etc
Game soundtrack is one of the best of Civ Series, i liked the menu music and the one that is played on modern age (sounds like matrix movie soundtrack)
And finally, diplomacy is the best one! Thumbs up! Positive points for positive relations and you get negative points for being arrogant, declaring war etc.