Good!
I didn't expect it to be as good as it was, so I'm pretty satisfied with this game. I like the backgrounds, and it was simplistic yet entertaining. Good sound, and original bosses - it would of been awfully repetitive without them.
My biggest suggestion is having "checkpoints", or at least letting you restarting on the same level rather than having to redo the entire game. Maybe even just have lives, so when you die you come back right away, but when you die too much you're done for. I mostly say this because I accidently died JUST as I defeated the second boss. So, when I should be getting full health for the next level, it didn't matter since I was dead. So, that sucked, and I didn't want to have to replay everything.
Yeah.
But 5/5 anyway.