Finally got around to playing it, and this game is super cool and really complete! I love it, definitely feels like something you'd see on a real gameboy from beginning to end. I went in blind and skipped the training, but even so could figure out how to use everything without much trouble! (Unless you can aim the boomerangs, I did not figure that out.)
My only nitpicks are that ducking doesn't actually reduce your hitbox, pressing up to climb ladders makes you switch weapon which players may not notice until they shoot something (I appreciate that nothing dies in one hit, so that didn't screw me over), and I'm a little sad there's only one ending. I tried bringing back nothing and still got humanity's praise, so I guess they just assumed there were no aliens out there.
By the way, I'm wondering if I ran into some bugs? Sometimes I could throw way more boomerangs than usual, and I have no idea why. I theorized it was coin-related but that didn't seem to be it. As well, at first when I messed up one of my capture prompts (on the RJ-numbers enemy), it would not let me input the final arrow despite having lives and 1 or 2 seconds left. On later captures I was able to do it... So I'm not sure what happened.
Note: While testing out various capture-related things, I accidentally died during a capture segment and it didn't break anything, so I'd say you still did a nicely thorough bugfixing job!