Forum member infinity has somehow managed to obtain a copy of Sonic the Hedgehog 4‘s soundtrack and has posted it on the forums!
My thoughts? Splash Hill Act 1 was just really shoddily done; this soundtrack is nowhere near as bad as I thought it’d be! I recommend checking out Mad Gear in particular as well as Splash Hill Acts 2 & 3. Really top notch stuff all around.
Check out the relevant forum topic!
UPDATE: Boss 1 is actually an unused track from the 16-bit Sonic 3D – so at least one track from this game dates back to 1995! See the below Youtube link for the original unused song:
An MP3 download of the above track is here.