A fun entry, but needs to scale up in difficulty. Once I got that hang of it, I only lost because I had to stop playing.
It seems like just going in a mostly straight line is the play to winning forever and if you get unlucky and hit by a stray shot, just heal from one of the big enemies that'll spawn right in your bullet path. Was able to hit over 9000 before I just had to stop. Hope you iterate on this more!