while it's normal for some menus to be missing in a prototype, I think that you should have volume settings and the ability to pause as soon as possible. the music is nice and fits the game well, and the title screen is amazing, but it also sets people's expectations for good backgrounds up, so take extra care with (re)drawing the battlefield. I also liked the powerup selection's flair and the enemy designs. personally I found the initial walk speed and heart collection radius too small.
on the technical side, I didn't encounter any bug or powerups interacting/behaving weirdly, but the performance declined noticeably with time and couldn't get to the 10min mark before the stutter got too bad.
as for the concept itself, I don't have much to say, this being a clone. if you added a twist to the genre I must've missed it.