The change I would make in Heroes 6 is to make the 7th creature a dark knight instead of a dragon. They removed it from the castle, even though it was stronger than the dragon in Heroes 3. And it wouldn't be a pity to lose the dragon =)

This person clearly hasn't played Heroes 3...:rolleyes:
First of all, death knights weren't stronger than dragons; dragons could age the enemy. I strongly criticize the developers for making such a weak dragon in Heroes 5, but I hope they will fix it in Heroes 6. And finally make liches a 1-cell unit.
And here's another thing. I would like them to remove this damn antimagic, because of it, many light races become cheaters, or at least have a way to quickly and painlessly remove it.