I'll agree with a lot of the other comments here, wherein my biggest complaint was the overall lack of spacial awareness that I really feel ended a lot of solid runs I had going. The angle just feels kind of awkward for something where very specific positioning is important to success. I think this problem was even more compounded once you pass the grassy area and get to the sky portion, which has basically visual indicator of where anything besides you currently is within the game space. The height bar on the left helps, but I do think that being able to tell where you are naturally is a lot more effective vs a UI element. Maybe a simple change of camera could do a lot of work in resolving the issue of determining your place in the world? On the other hand, I did like how the angle made it feel somewhat more cinematic. Perhaps just keeping some form of ground visible in the world, which really seemed to help in the first portion of the game? Maybe clouds, or anything that would let me see where I am. Just a bit of research into Zaxxon, and it looks like you could always see the shadow of the player. The aspect ratio also threw me off a bit at first, and I wasn't sure if the game was imagined being played on a mobile screen?
As for the visuals and audio, they were great! The simple 3D aesthetic really felt cohesive. Very whimsical, and I totally could tell I was grinning through each of my playthroughs. Just a fun ad relaxing vibe, which is what I think you were going for!
I was also really impressed that you managed to fit in a boss battle. I only made it to the boss once before dying and running out of steam to start over, but it really helped make the game feel a lot bigger and more epic.