Sorry for the delay dude(i'll reply you in an expanded way in my comments, but thank you so much for your feedback):

general observations,

i personally loved luftrausers on release, and it's cool to give that gameplay a new spin

- if you are making this game as a commercial product:

so far i did't see enough to be considered a new spin; you know, the classic it's like "X but". the rogue/survivor could be enough, you can't never say.

for what i know the classic ways to "redo" a game is the blizz way, aka X but iper quality; or the "it's X but" i named before. Imo it's pretty hard to compete against a vlambeer game on quality side, so my overall tip is for you to make that design yours and expand/remove stuff in a way that follows your sensibility.

-if this is a game you are making just for fun:

imo cloning a game you love it's a great way to upgrade your devving skills. my only tip is to code in a way that make your stuff reusable in the future. after a few projects like this, your toolbox will be full of scripts and other stuff. at that point making a game will be so much faster and easier.

random stuff i noted

- on first start, the game has problem with a dual screen setup (1080p). the game app will stay on screen for maybe 1s, then autominimize and fuck up the start bar etc. 

just removing the fullscreen fixes it, but it's a bug that some "real games" also have.

- lmao the second lavel it's in a desert and we dive in like tremors; 

- i find funny that clouds are obstacles that block lasers (i'm personally a fun od obstacles in general, so maybe think an evolution of obstacles that become more and more dangerous)

-  i did a few test on your issue: if you go in the "ceiling" enemies will bug out and wont spawn anymore. On my end, that happens every time on level one; you must have a trigger that kills enemies that go there, but when that happens you don't trigger your "spawn next enemy" method

- the background is too bright and can cause confusion on readability of the screen. Yes planes are green, but you need to consider colorblind people. 

my classic advice here is to set your devving screen in b/w and see how constrast is a problem; since you game is pretty fast, everything needs to be clear at first glance. not only colors/contrast but also shapes

First Impressions:
The parallax and movement look really nice. What are the controls? Is it locked to 60FPS? Movement seems a little blurry

After thoughts:
The first level was too easy and I got bored chasing for enemies. I thought that was it, but then I saw a screenshot of the second level on the demo page. That one was better, but now I was being swarmed by enemies I felt useless against. Maybe a better loadout would have helped me fight, but the issue with the laser is you have to face an enemy directly, which is kinda boring to do when moving around and dodging bullets seems natural

What I liked:
I liked the animations and parallax world

Something that didn’t work as I expected:
I was hoping there would be pick up or recharged, or more of a linear level bullet hell-like combat.

I have no idea how to play this game properly. At first my instincts told me I should try to find an opportunity to turn around and take down chasing enemies, but the camera and movement aren't fit for that. In the end the most efficient playstyle is circle strafing and holding the laser, and waiting for most things to die. The shield regen communicates that it's not a tight game and you are expected to get shot very often, and also allows you to play defensively by buying time for the shield to refill.

The laser is kind of an unfun main weapon for this type of game - non automatic high damage weapon or dropping bombs could be better, and laser should be for players who got the hang of aiming and movement. You should probably ditch the upgrades for the time being until the base gameplay is tighter.

Visuals make everything hard to make out, enemies are nearly invisible with the mountains in the background. I also can't tell when I'm taking and connecting hits, that's also a part of why my playstyle instantly turned sloppy.