This is a very neat, very cute little game.
I liked the idea of a 2.5D bullet hell a lot more than I thought I would. The core gameplay loop is solid, and I found it surprisingly fun. I do think the wave attack needs to be buffed; most enemies are bullet sponges and the wave has far worse DPS. I didn't use time slowing at first, but started playing with it more and more. I think I stopped playing before it would have become really useful, but I'll get to that later.
The menu is broken at 4K, showing the graphics in the middle surrounded by the default skybox, with the controls screen showing in the bottom left. This seems to be a known issue.
The sound design is a mixed bag. I like the background music, but it sounds suspiciously familiar. The 8-bit bloopy shooting sounds are really at odds with the other sound effects, which are a more realistic style.
I wish I knew what I was fighting and why. I don't think this is necessary, per se, but I prefer more narrative/story driven games. So maybe more of a personal preference than anything else.
Unfortunately, there seem to be some performance problems. The game started off running okay, but I was only able to play to wave 5 before the framerate became so bad the game was literally unplayable. My laptop isn't the fastest in the world, but looking at some of the other comments I'm not the only one having this problem.
I think if the performance issues can be solved this would be a pretty good game. I'd like to see some other things tweaked, too, but the performance degradation is a much more critical issue.