Stages could use some backgrounds, music is not really fitting in some levels, some collisions were pretty much unfair (I'm mainly talking about the spinning spikes from the deadly Mechanorab fight) and I didn't like the gungames logo on every screen, but the game was still great. The bosses were fun, colourful and bubbly, which took me off guard when the Hemotron 5000 happened (my favourite fight by the way <3)
EDIT:
I've got all of the achievements now and it was PAINFUL, so yay for me :D