Not too bad, but not exactly authentic.
Overall it sounds pretty good, though maybe a little too busy. But one thing people forget when trying to go for 8-bit remixes is the number of channels normally available for 8-bit.
The NES allowed for 5 sound channels, for instance, while the Gameboy (also 8-bit) allowed for 4.
This sounds like a lot more than 5, so...yeah. Authenticity is hard sometimes, but I might recommend you give it a shot.