I liked the art style, and I agree that hitbox was inconsistent, I noticed it only counted when I tried hitting when the thing drawn in forehead was inside the box.
One suggestion I would say is that make it, even if a little amount of card is inside the hitbox, it counts, but if that drawn thing in forehead is inside the box, we hit a perfect and something special happens, that way it won't be much punishing to beginners while allowing experts to shine through by hitting multiple perfects.