Civ 4 is fun, I still remember playing as Romans and pwn people with my Unique Unit. They just don't believe their eyes when they have only like 2 archers defending their towns against my horde.
Apart from that serious balance issue with Romans, I don't particularly hated the Civ 4 combat system, you just need to bring some catapults/trebuchets to win. It is more a trouble fighting an AI, sometimes.
I am not very optimistic on hexagonal tiles, I think squares fits better in human brains. (it is impossible to construct a stuff with simple shape with merely hexagons.