I think the main key feedback is more levels with higher difficulty- the first run I unintentionally didn't realize I could use the power ups and just managed to beat all but the last lvl with the base projectile.
second run I realized I could and every one had a kick-ass soundtrack attached.
So more lvl's- more difficulty (by larger lvl's more enemies would have helped a lot!)
also indicators that you get to use the fancy effects would be nice.
also fun to see the entire project is open on git! :D Well done guys!