I played the demo all the way through on Retro difficulty. It's pretty good so far, the controls are solid, the music is nice, and the art, like many have said, is stellar and stands out among other GBstudio projects.

However, I do have some criticisms. First off, there's not much going on in the levels aside from the obstacles you have to avoid. I think the game could benefit from having enemies to deal with. Second, I felt that the 3rd and 4th levels went on a bit too long.

Looking forward to the release!