Really great job with this game -- very nice palette and artwork (my favorite part), the music is great, the mechanics work well and the selection menu looks very professional. As a heads-up, on Planet 2, I accidentally walked off the right-hand side of the level, fell to a platform off-screen and couldn't get back up -- I had to restart the whole game, so if you plan to update it, you might add a collider over there. Very minor issue.
Great job!