I find this so accurate to the style that at first it gave me an uncanny valley feeling of “hey, is this a copyright-free spoof of one of the ACTUAL tunes?”. Then started to warm up and enjoy it a lot. I think you nailed it!
Soundwise, I can’t believe that this is musescore as others said. Bit fizzy, not too bright, but also not abrasive. In the end that I call a “rendering issue” and who’s to say that an actual gameboy on low volume wouldn’t feel like that.