I should have checked this game out sooner, it's SO good!! Like, seriously, this is awesome, and it's SO accurate to the GB!
It didn't just stick to the colour and resolution limitations, you went full-on with respecting the system's specs, no extra layers that the system didn't originally have, the sprite colour count is correct, the palettes stay consistent with only 4 colours, and even the mid-game changes in the palettes could have been done on Super Game Boy (though I'm curious as to how you'd have planned on achieving a day-night cycle on the original GB), and you even paid attention to less noticeable details like dialogue boxes being fully opaque and covering up the entire horizontal resolution, this is perfect! Even the movement is tile-based, though you might have gone a step too far with that in locking the sprites onto the 8x8 grid, you know, GB sprites can move freely, but this is no less accurate! (Though it reminds me a lot of old Japanese PC action RPGs like Ys for example, though since this is flip-screen it reminds me more of MSX games...)
The one aspect of your game that isn't totally accurate though is the sound and music, it sounds more like a PC engine than a Game Boy, that's the one thing that keeps me from giving you the full 5 stars on Gameboy-ness... You still get the full 5 on Fun though! Good job!