Not bad, but a few issues with originality.
Controls: A little loose and could use some polish, but overall, not bad. Makes sense for a platformer.
Graphics: Again, could use some polish, but not bad overall. However, you might want to talk to your artist about this: Your main game sprite is from the Flixel collisions demo (as seen here: http://flixel.org/flxcollisions/). I don't know if this was intentional or not, but you might want to put Adam Atomic's name in the credits. Taking credit for other people's art, whether intentional or not, is not cool.
Sound: Nothing to complain about here. The loop gets a little annoying, but other than that, nothing that would otherwise distract from the game.
Concept: The split-screen thing isn't completely original. I played something that's almost identical about 3 weeks ago. But I do like the twists that you've added (getting rid of the bottom screen by passing through a green door). Gets a little boring, but not too bad.
Conclusion: While the gameplay is addicting, it does need some polish. However, I am knocking you mostly for using Adam's sprite without giving credit where credit's due.