Sonic 4 Episode II the new and continuation of the Sonic 4 franchise and still can't seem to get the right footing when it comes to attempting to mirror it's Sega Genesis days. With this episode your faithful side-kick Tails returns for some fun but the fun isn't quite enough to save this title.
To start on the more positive end, the physics have been marginally approved over Episode I's sloppy physics. Sonic won't be getting stuck in loops or on hills this time but Tails certainly won't be a great help in carrying you. The levels are actually original this time instead of rehashes from past games the way Episode I did and bosses aren't rehashing either.
The one exception is the Special stages from Sonic 2 which aren't dazzlingly confusing with per-rendered CG Graphics but aren't any easier as ring placement and the still slightly sluggish physics make it difficult to collect rings.
Negatively the game falls short with Tails. You are forced to carrying him along for every stage. No Sonic alone stage, no Tails Alone options just forced to group up. There are a number of puzzles which involve precision timing and grouping of abilities. Most of these are relatively easy for the most part but there are areas where puzzles are just plain cheap.
Bosses are also cheap as most of them require Tails the less than polished flight mechanics make it difficult to attack Dr Eggman and the game more frustrating. Metal Sonic is in the game but feels more like a last minute shoe-horn in due to the success of Generations. The DLC Episode Metal is pointless as it's just Episode I with Metal in place of Sonic. I guess I can't complain too much on that as it was free with owning Episode I, but if somehow you can purchase Episode Metal, don't.
Two Player is best avoided. In this game Tails in Two Player Mode is linked to Sonic (which was actually in the Beta Version of Sonic 2) thus if one of you dies you both dies. Only play Two Player if you want to grief your friends.
Sonic 4 II isn't anything special. The very least it was cheap and not a waste of the $55 like the padded out Generations game. The bosses are cheap, the stages have cheap traps, Metal Sonic was clearly thrown in at the last second. The graphics are nice, the physics are slightly better, but the music is still substandard. I don't even want an Episode III now, it's probably for the best it's not in the works any time soon.