Hey there, I'm liking the demo so far. I see you are close to releasing another demo, so this feedback may be irrelevant by now.
I haven't completed the demo, because I got stuck behind a pedestal that had my second missile pack on it. I cannot jump back out. I can provide a screenshot to show you where if you need it. I will need to quit and reload from a save.
I noticed many scaling artifacts in the intro sequence that look like textures are being stretched in a non-1-to-1 fashion, even though my graphics settings were set to not stretch.
The 'fit to screen' option leaves large black bars on all sides of the game area. I assume you are doing integer multiple scaling only - a 'keep aspect ratio' type scaling could eliminate the black bars on two sides of the screen (top and bottom in my case) and would be an improvement.
I tried running with vsync enabled. I usually prefer this to avoid tearing artifacts. However, the game ran very sluggishly. The built-in fps counter says 30fps, but it seemed like the game logic (rather than rendering) was executing perhaps somewhere in the 8-10 fps range.
Looking forward to trying the next demo!