If you require full screen mode so much it would be better if the initial windowed mode would be smaller so one can get the "set to full screen" button more easily.
The first time in windowed mode it stuttered at times and didn't react to my inputs for a moment and then the ship jumped a bit, which made it somewhat extra difficult. Second time in full-screen mode went much better, but sometime around level 5 (I think) my shooting performance really dropped and I couldn't practically crack any asteroid anymore because I could not shoot at them often enough. Was this intentional as a difficulty ramp-up or a bug?
Movement felt slightly jerky at times but (appart from the windowed-mode stuttering on my first try) fine.
As for the gold nuggets not dropping quickly enough, flying up to them to grab them helps a lot ;)
What exactly does the scanner mark? At later levels there are rocks that don't get triggered. At first I took it as "this rock is invincible / too hard to crack" - until I shot one.