The movement is currently "very fun" it's very snappy and reactive. it took me a while to realise I could dive when mid-air but when I did, the game became a lot more trivial. The upgrades provide some replayability but without a high score screen I have no idea how good I'm doing compared to myself or others. Numbers go up but since looking at the numbers has the risk of colliding into something, I found myself not really doing that.
I found collisions a bit too jarring, they pull you back from "oh my god this is amazing" to "oh wow this is slow" and every time it's a bit of a grind to get back up to speed. I think it would be nicer to, as time goes on, recover faster and faster from these collisions. Especially with the heart and shield drops, it's not too hard to be functionally immortal if you have a few well timed crashes. Which means the pay-offs of a high-speed run are not as great as they maybe could be?
Art is fun! Particle effects or screenshake could maybe spice things up even more, but your sprites are great.