It's a slight improvement upon Episode I, but still lacks the charm of the classic games.
Storyline:
Directly after Episode I Sonic and Tails are off on another Adventure. Nothing new here, until they realize Metal Sonic is back and Little Planet is back in orbit. Sonic, realizing Eggman is involved, tries to stop him.
Gameplay:
The core gameplay in itself hasn't changed much here. Aside from some Tails specific ability (tag actions), there's nothing really new. Though the physics have been improved considerably. The level design though, still isn't there for me. The special stages here though, these are the half pipes from Sonic 2. They're all fun up until the nightmare that is Special Stage 7. I redid this stage multiple times for about 4 hours until I finally got it.
Graphics:
This is a GREAT improvement on Episode I. The game runs smoothly, is colorful, and is just really pleasant on the eyes. No complaints here.
Sounds:
The soundtrack is........ well...... eh. Instead of dying cats this time we get dying ducks.
Bonus:
If you have both Episode's I and II on the same console, you unlock Episode Metal. It's Metal Sonic going through the Episode I stages backwards. It's okay.
Overall:
This is still a fun game, but it isn't as big of an improvement as one would hope. Sidescroller fans might want to give this one a look though, it's one of the better ones out there.