as long as they keep making games in all the styles they have made before, i will be happy.
that being said, i'd probably be most happy with a new game in the Castlevania: The Adventure ReBirth style where there's multiple paths through a level and there's extra lives etc. But I'd really like them to add CV III style multiple characters to it, or enhance the weapon system of the main character so that it can be different every time you play.