Let's start with control and physics, I'm presuming you're playing on the Xbox 360 so if you're playing on the PS3, PC, an iDevice or Android look somewhere else. You move Sonic (or Tails) with the left analouge stick and jump with the A button. Pressing the A button again in mid air whilst no enemies or springs are on screen causes Sonic to air dash, helping him build up speed faster. If there is an enemy or spring on screen pressing A again in mid air will cause Sonic to do his Homing Attack, which works basically the same as in Episode I. At certain points, Sonic and Tails will have to use team attacks to overcome certain obstacles. The flying attack makes the game wayyy to easy as you can save yourself from certain doom just by hitting X. The physics are improved and feel way nicer. Sonic no longer does a "huzzah" pose after coming off a slope and rolling can now help you gain speed. They're not perfect but they are better than Episode I's. Also, Super Sonic runs off of Episode I physics. I don't know why.

The graphics are much better than Episode I's, as the game now uses full 3D environments instead of just 2D Cutouts. It runs really well and the environments look really well polished and nice. Cutscenes are okay-ish I guess.

The sound is by far the best part if the game, as expected from a Sonic the Hedgehog game. Metal Sonic's theme is by far one of the best songs in Sonic 4 as a whole. Sylvania Castle's act 1 theme gets you pumped for the journey ahead. A really good soundtrack, love it! 

If you owned Episode I (Excluding those on the Wii) you'll be happy to know that buying Episode II gives you a bonus story, entitled Episode Metal which is basically Metal Sonic going from Stardust Speedway junk to the great anti-sonic he once was. It's an okay bonus but it's only 4 acts long with a little up in difficulty. I give SEGA credit for trying to revive Metal Sonic though. Episode Metal is just there to help expand Episode II's lifespan and it's kinda underwhelming when you think of it like that. Anywho, Episode II is not a long game. It's only 12 (technically 13) levels long and the only reason you might need to go through it twice is if you need to get those Chaos Emeralds.

Story is simply Eggman has taken over Little Planet and is constructing the Death Egg mk II with it. To help stop Sonic, Eggman rejuvinates the dead Metal Sonic (via the power of POINTING might I add) and the two team up to stop Sonic and Tails. Simple as.

Not a very deep game, but Episode Metal helps increase the games lifespan slightly.