I personally think that many many aspects of RTW is better than MTW. One of the best examples would be the new campaign map system, which makes the game a LOT more challenging to a lot of players - it makes you think on an entirely different strategic level compared to MTW.

I also like the sieges in RTW - manning the walls is cool (even though the computer utterly sucks in attacking stone walls because they get shot to pieces by the defensive towers, i think its very challenging to attack stone walled cities playing as some factions. If you got the time limit on anyways)

Although the battle-field AI may be lacking at times... i think its not horribly terrible. Just bring smaller armies when you're attacking. The battlefield diversity is a really good improvement on MTW though - rather than having some unique units for the different factions, there is virtually a different tech tree for each faction. This makes it so much more enjoyable and a lot of different playing styles originates from that.