Sonic's back with a BANG!!
Story: This game takes place right after Sonic and Knuckles. After Sonic destroys the Death Egg and Angel Island returns to the sky, Sonic decides that it is time to take a break. After parting with Tails and Knuckles, he sets off alone to explore new places. However, Sonic didn't know that his nemesis Dr. Eggman has survived their last encounter, and has revisited and revised some of his "very best" robots to finally beat Sonic once and for all.
Gameplay: The gameplay is just like Sonic 1, 2, and 3. Some of Sonic's old moves return, like the Spin Dash. The Homing Attack is in this game too, and actually for a reason. Some parts actually need you to use it to continue on in the level(s).
Difficulty: This one really depends. If you just want to breeze through the game, its fairly easy, only with some parts that are a bit challenging. If you're going for Trophies or Achievements, then the game is a notch or two harder. The final boss is kind of annoying, and is unnecessarily difficult compared to the rest of the game. It is also unnecessarily long.
Music: Two words- Utterly Fantastic.
Overall: This is a pretty good game. Even though it is only Episode 1, it could've been longer (it has 4 Zones, and has 16 normal levels, 1 final boss stage, and 7 special stages). Besides that, Sonic 4 plays, and feels, like its classic counterparts. And its worth your $15.