The thing I am most anxious to hear about is the philosophy in developing the AI. Truly, the visuals, the towns, the creatures, the campaigns, and all the rest matter little if the AI is not up to snuff.
Most of us noticed it in IV, but I had a sense that the AI had become subtly more forgiving going from II to III, and definitely from I to II. Really the original HOMM game put more pressure on the human player than any other turn based strategy game I can remember -- even if it did so by magically knowing the location and occupants of your towns.
Two things seem to add to gradually weaker AI as time goes along:
1) The broader the audience, the less the average customer wants to have to think deeply in order to win. On general forums, I heard many people say that they liked the easiness of IV, even the initial release. Of course, these are people who buy a lot of games a year, play each for a few hours, and then move on. And they want a winning experience during that brief time. Those of us who want the game to still be a serious challenge after a hundred(s) of hours of gameplay have a whole different perspective.
2) The more complexities added to the game, the more difficult it is to write a good AI. A game that offers incredible depth of choice for the player sounds good when it goes on sale, and it may make for a great multiplayer experience, but if the AI cannot use the choices intelligently, it's going to wreck the game. This can come in two flavors: the fatal flaw and the generally brain dead. HOMM IV failed on both accounts -- the fatal flaw of losing AI heroes to independent armies, and the general brain dead lack of aggressiveness to provide meaningful competition.
The usual method of "difficulty levels" does not work very well because it is based on things like starting resources. Such a system makes the beginning of the game mor challenging, so there is a tense stretch when you know you are behind -- but you soon catch up, and the tension is gone for the last three quarters of the game. VERY few strategy games have avoided this.
So I am anxious to hear what this team has in mind. How do they plan to develop AI that reverses the sad trend in HOMM and return to a game that maintains tension beyond the opening weeks?