Great job!
What I didn't like (it's a minor thing, but) is the icon backgrounds. The default ones have artistic backgrounds from the mod, but the new ones don't!
Also, in my opinion, I've never seen the point in having too many different creatures/heroes. You'll never encounter them all, and the balance will be annoying xD
It would be very good to use this later in Heroes 8, if there will be one, of course.
The engine would be the same as in Heroes 5, but there would be new features and other interesting things, and new creatures based on the creatures from Heroes 5?