There were a couple of things I really liked here. There was a faded out face I think in the background - just barely noticeable. I liked it, not sure why.
The upgrade selection animation - with the music slowing down...that was really cool and added a cinematic feel to the moment. I wish the play had paused or slowed down while it happened as well so I could pay more attention to it.
The boss seemed a bit tough, though I suppose it depends on your upgrades!
Cool game!