Awesome Job :D Had the game on my wishlist on Steam for quite a time now, but discovered just today, that there is a demo from you here on itch.io .
So far I really had much fun with the first level. Especially movement and gun (impact) sound responce felt brilliant (many modern Shoot 'em ups and FPS lack this kind of "oomph" regarding collision, gun fire and projectile impact response, but you totally nailed it).
The only criticism I have so far is, that the textbox speed of messages was too fast and therefore the messages disappeared too quick for me to read comfortly. A slider or some kind of option to adjust the textbox speed would be a great QOL-improvement in this regard, especially for non-native speaker.
Regarding movement, maybe you could implement something like a fast sideward jump to better dodge enemy projectiles, but that is pretty nitpicky from me, especially since I don't know, how you will design the progress of the mech via upgrades, etc. .
All in all I'm really excited for the final release on Steam and I can't wait to see more and play the full game. Keep up the awesome work :)