The next game should have either a daul-button combo system (like in LoI) or a time-enabled combo-system (DMC 3 +4). Also, there needs to be some sort of innovation combat wise, be it more pokemans or something the player is actually in control of (easy-way=grappling techniques, hard-way= anything I can't think of, aka: surprise me).
The game should also have a difficulty setting option available from the start (Easy, Normal, Hard, Extra Hard), so there's no excuse for making a game too easy to cater towards a specific audience.
Lastly, try to stay low on repetition environment and enemy wise.