I thought this was fun! I didn't notice the upgrade arrow until a ways into my first run. The way the music pauses is a bit strange, and a lot of things could've used some more sound effects. I wasn't really ever in love with the controls and it felt weird being able to be and be shot off the sides of the screen. Also the fact that the missiles couldn't be shot was kinda disappointing, I don't know why I automatically assumed that would be the case to be honest. Can't hold it against you but I do think it might've been better if you had a way to deal with them besides running :)
overall this is a fun game, the upgrades feel good, buying health back is annoying but not so expensive that it feels punishing. Good work on this!