Controls well, looks great! The UI is a little hard to read unfortunately, but some of that is just it being 4 colors.
The music didn't really feel fitting to me. It might have worked better if it were more like a Game Boy chiptune? I'm not sure, but the vibe I got was more like the SNES game B.O.B. than a GB space shooter I think.
The mutant and asteroid sprites are great though. They're not too big for the screen but they're still nice and big and they look like what they're supposed to be, which is always impressive on a small palette and a small screen size. Great job!