Very conflicted about this one. I personally would consider it better and definitely more original than the first one (which was pretty much based on a Sonic 3&K style) but there's some really odd design choices that stop me from giving it a higher ranking.

The boost formula makes for a more fast paced, intense gameplay and encourages you to replay the stages in order to completely blast through them, once you've learned them.
The new moveset for every character is also a great addition, Sonic's in particular being the one that rewards high skill gameplay and reaction timing.

On the downside, the game is heavily based on trial and error with a bunch of bottomless pits that are an instant kill and some really cheap boss battles. Exploration also suffers a lot, backtracking is usually near impossible depending on which character you're using and forces you to either die or replay the whole stage again to have another try in order to grab all the special rings which are required to enter the special zones and get all the chaos emeralds.

Still, i'd definitely give it a try i you haven't yet, it's truly one of a kind, i just wished it was a bit more polished.

Oh and the music slaps, as always.