I pretty much have only ONE worry about this game so far.
My love for the original series of Megaman stems from how damn well suited the original Megaman sprite was to the physics of the original games (8-bit). In my favorite game of the series, Megaman 9, the jumps, platforms and shooting are EXTREMELY well positioned, because the character's sprite is the exact perfect size to traverse these levels. The Megaman series is pretty much the one game series I can make a pure thesis of how the main character's sprite size, hitbox and movement capability's direct relation with the enemies, hazards and levels is in absolutely perfect harmony. Not only that, but they remain the games I will not complain about the lack of shooting up or ducking, specially because the character's size and manuverability felt perfect the way it was (not fond of the sliding myself).
Megaman Powered Up is a very fun game. It's actually one of the Megaman games I truly like, along with the original series, Maverick Hunter X and the original EXE. I remember having quite a bit of fun with it over a holiday, and it's a very smooth and tightly made game. But it doesn't work as well as the original series did. Replacing the original sprite with a big-headed doll threw away the balance I used to have with the game, and made me play it in a bit of an uncomfortable way at times. I loved it as a stand-alone game, because it felt like a way to truly fix the first Megaman game (which I have some issues with, MM2 was the first to really get it right) and it was very fun to play.
But using this style in a new Megaman game, specially made for EVERYONE to enjoy the Megaman series? This is a big title, I think. And I kinda think they're throwing everything away on design. Heck, maybe I'm completely wrong and the big heads are just for the few characters I've seen, maybe I'm making a complete idiot of myself here. But if I'm not, I think this is really gonna stunt the enjoyment of this game.