Satisfying game, with great menu animations. Seriously, the way the game starts is just *chef's kiss*. Jumping feels really nice, and the shooting does exactly what you expect it to do.
I do have one issue, sometimes I would get hit by one of those red spinny things, which damaged me, took me to the upgrade menu, then immediately hit me again. Some invulnerability after you upgraded would be very nice. It doesn't have to be long, just half a second is enough.
Anyways, solid game!