I've always thought that one of the key features in the success of the HOMM series was the ability to create user-made maps. Its this feature that made them virtually infinite games.
I made a few maps in H3 and really enjoyed it, but I never made any for H4. Now, partly that was due to sheer laziness, but it was also because the really good features in the H4 editor were so user unfriendly and so easy to get wrong.
Don't get me wrong. The features in the H4 editor were incredible. They are so much more powerful than H3 that the potential to create really good maps was certainly there - but you had to be ****ed near a professional programmer to use them effectively. That's why Qrystal was able to sort them out - and make some great maps - but I never bothered to learn.
So, top of my wish-list for H4 is an editor with the power of the H4 editor, but the user-friendliness of the H3 editor.