Things I like:
*Oda Nobunga as a Japanese leader. He was really the one who reunited Japan, whereas Tokugawa was just his general.
*Needing multiple occurrences of a resource to produce more than a certain number of units that require it. Good, realistic, and should make for some fun wars in the modern era!
*At least cities have their own means of self-defense. Yeah, see below.
*Unique soundtracks with for every culture.
*Licensed music, which hopefully means good, actual modern music.
*Expanded flavors.
*Better leader graphics and personalities.
*Reseach pacts.
Things I don't like:
*One unit per-hex. I remain a huge skeptic of this, even when IGN touches upon the positive side. While I hate stacks of doom as much as the next guy, I still think it's incredibly unrealistic to implement this in a game of this scale, and furthermore, it has the potential to remove the realistic military advantage Civilizations like Russia and China have; that is strength in numbers. It could be a terrible game if one unit that starts out stronger than any one unit the enemy has defeats the nearby unit, levels up, and heals all before the next fight, doing the same thing over and over and becoming stronger each time.
*Catherine as a Russian leader. Sure, she was a noticeable reformer, but she still is in Peter's shadow.
*Axing religion. To be fair, it wasn't done well in Civ 4, as it isn't realistic for Justinian and Suleiman to end up with the same religion and have no reason to fight each other. Nonetheless, removing it is liable to make things even less realistic.
*Those city graphics. They had better be WIPs, because they look like crap.