Sonic Fan Remix is a 2.5D game by Pelikan13 and Mercury, creator of the "Sonic Physics Guide." In this three level demo, you get to experience a re-imagined Emerald Hill Zone. Act 1 and 3′s layouts will seem familiar, but Act 2 is entirely original. What's also unfamiliar is the crazy amount of detail put into this project. From the water/rain effects to the game's lighting, this is truly Emerald Hill as you haven't imagined it.
A welcome addition to 2.5D Sonic are the original physics that made Sonic a hit in the first place. There are even a few adjustments to suit Mercury's tastes.
About the whole "rolling off a cliff onto a badnik rebound height" thing:
I didn't really like the way classic Sonic physics handled this. If holding the jump button is what makes Sonic rebound, then that should happen in all cases. I don't like the fact that in some cases the player has no ability to cut the rebound short by releasing the button. There's no homing attack or anything, so you can just hold the button down as you hit the enemy to rebound.
In other words, the change was intentional.
A second intentional change is that Sonic can control the trajectory of his jumps even if he jumps while rolling. Sonic CD is the only one of the classics to do this, and I find it vastly superior. In fact, I can't imagine why the other way was ever used - what's the logic behind it?
Some of the physics inconsistencies aren't intentional, though. Unity can be a pain sometimes, and I wasn't able to make everything as accurate as I'd have liked. (For instance, the camera isn't accurate to the classics yet.)