I really like the game, there are a couple things that would improve it even further IMO.

#1 The ring of enemies right at the start, get rid of it. Very frustrating to not be able to orient yourself for a second and immediately starting the run off by taking damage.
#2 Increase the amount of enemies over time. Fells like there is no difficulty curve, or even a negative one where it gets easier over time.

Other than that there is great variety in enemies, the perma upgrades are motivating and give you this "just one more run"  feel.
Fun game.