You should include a legacy of which power-ups are which, because the game is too frantic and the power-ups are too small for me to easily figure out on my own. I say this because I would like to avoid getting those blue bullets.
Other than this, though, I have to agree with cudameister: it is surprisingly addictive (particularly considering how bad I am at it.
I would definitely add some variation in the background images and even platforms. Overall, though, besides needing a lot of polish and more challenging levels, it was rather fun.