From 2 seconds with this proto I've already discerned that Hyper Sonic, while implemented, has a constant circle of stars around him, though not in the same style as the Invincibility powerup.
The intro to Mushroom Hill does not appear to have been implemented yet; Sonic and Tails begin standing in mid-air and simply fall to the ground. The Hidden Palace scene when you enter the Special Ring at the beginning of the stage plays Death Egg Act 2 music, unlike the zone itself.
Sonic does not fall under the sand and pop back out in the intro to Sandopolis; he merely falls from the sky and lands on the ground normally.
Lava Reef 2 does not have the screen locked at the start of the level as in the final when accessed from level select. The lava is not cooled off at the start, but the zone uses the same blue palette as the final at this stage in development. Lava Reef 3 (Sonic's boss) uses the Lava Reef 2 music as opposed to the Boss Theme used in the final.
Hidden Palace still has Sky Sanctuary Music - the row of monitors near the top of the level still contains an S monitor instead of Speed Shoes like the final, but the row of monitors to the right is now two Super Rings and a 1-up like in the final (as opposed to Sonic 3C 408's three 1-ups). There is still a Fire Shield next to the teleporter that takes you up to Knuckles, instead of the Super Ring that's there in the final. Knuckles' boss still plays the Sonic 3 miniboss theme. The scenes after defeating Knuckles occur pretty much exactly as they do in Sonic 3C's 517 beta, but as in the final Robotnik no longer flashes when hit by Knuckles.
The Doomsday Zone automatically starts you as Hyper Sonic when accessed via level select, unlike the final where you are Super Sonic if accessed in this way. The zone's background also has a different, greyer pallette, and the zone scrolls a LOT more slowly to begin with - you can speed up the scrolling by holding right to gradually accelerate it, but hitting an asteroid will slow it down again. No SFX plays when breaking the asteroids. When the boss reappears after its' blue armour is destroyed the 'badnik popped' sound effect plays instead of the sound played in the final. XD
Hidden Palace Zone is accessible from the level select - as are all the Sonic 3 zones, bizarrely enough, considering this is a 3B proto not 3C. Knuckles' theme tune is the version from Sonic 3. The Sonic 3 Miniboss music is also still in the Sound Test and used for all Act 1 bosses and the Knuckles Hidden Palace boss. The invincibility / Super theme is from Sonic 3, however the title screen theme and 'game complete' jingle are both the versions from the final Sonic & Knuckles.
I'm off to explore this a bit more - will update this post if no-one posts before I find new stuff; if not, will post a new post with more info. =P
This post has been edited by McAleeCh: 23 February 2008 - 07:52 PM