Great job! I liked the difficulty settings, they were well thought through, and the way the theme was implemented was pretty interesting.
I do have a few issues ;) none of them are huge, but I think if you address them all you'd have quite a fun game on your hands!
- the UI doesn't scale very well at all. Are you using Text Mesh Pro or just the normal text components? Use TMPro ;)
- Movement was waaaay too slow. Double it at least
- To offset the faster movement, make everything faster. Like, absolutely everything. And add loads more bullets - the point of the game is dodging, right? So let me dodge things ;) I get that the first few levels need to be easier, but you can still pretty much double the amount of things you spawn. Felt like I was waiting around quite a lot.
- The player character had a weapon, so I thought I could use it!
- Check out vlambeer's talk "The Art Of Screenshake" (or 30 things to make your action game better) Overall though, you've made a neat little game here and should be proud of it!