I really like the ideas present in this game. Anything that has on rhythm/beat stuff is great.
I know this is just a game jam game, but something that analyzed the music more and didn't fire or spawn enemies during the times where the music was slow or off would be nice. It was odd just having the firing during the quieter moments. Although, this would leave the player with nothing to do.
I didn't really see a point to the combos as I don't think I was doing any more damage than before, but it was a nice indication that I hadn't taken damage recently.
Some mechanics, items, or anything different than the music/layout would've been nice on the other levels, but might be a bit beyond the scope of the game jam time.
Very nice job though!