Neo Sonic the Hedgehog is a mostly layout-based hack with a few other changes, including palettes, art, ASM edits, and a few other things.
As of now, only layout for GHZ has been done. My aim is to eventually complete layouts for all zones, but I'll have you know that layout editing is a time-consuming process (if you want to make it look good, at least). This hack also uses MegaPCM, therefore, the DAC samples have been changed. (Also, listen to Spring Yard's music and you may hear a small difference in one of the instruments.)
Now, for some random credits.
Selbi - For Sonic 1 - Text Code Generator MainMemory - For SonLVL Stealth - For SonED2 Vladikcomper - For MegaPCM Probably some others