So basically every boss belongs to a different "game" and each game has a different gameplay?
That's not confirmed at all, it's just wishful thinking from certain people as far as I'm concerned, so far it seems the core gameplay is what we've seen, a simple arcadey top down hack and slash with a couple cooldown special powers, maybe with some racing level or whatever thrown in for good measure to break up the pace of the campaign and other separate modes like the "adventure mode" which sounds like a visual novel explaining more of the story. Until we actually see gameplay footage that could be a primary gameplay method across a given world (so not the car thing teased in a video) I'm sticking with that idea to not get disappointed if it's found out that, indeed, what we've seen is the core of it all.
I like what we've seen so far anyway, as long as the level design, enemy design, encounter design, and boss fights escalate throughout to keep players challenged and engaged.