The trailer looked a bit plain, but I can imagine how fun this will be once it has enemies. I really, really, really love that background.
A few suggestions though:
1) By the looks of things, the bat's movement had no effect on Kirby's speed. I think it would be good if when the bat was moving left and Kirby hit it, it gave Kirby a bit of 'left' momentum.
2) Different types of blocks, though I'm sure you've considered this already.
3) A better 'block disappearing' transition. Not too keen on the current one.
I want to play it. Now.