Sonic the Hedgehog 4
From Sonic Retro
Sonic the Hedgehog 4 is a Sonic the Hedgehog episodic game with its first episode released on October 7th, 11th, 12th, and 13th in the US regions, October 7th, 13th, and 15th in the EU region, and October 12, 13th in the JP region. It was originally codenamed Project Needlemouse, after Mr. Needlemouse, the name given to several early prototypes of Sonic.
On March 22, NGamer revealed that the game will have 3 Episodes, each comprising 4 Zones.  Each Zone has 4 Acts, the last of which is a boss battle with Sonic's perpetual nemesis Dr. Eggman. This is the final game of the Death Egg Saga.
Sonic the Hedgehog 4 is set shortly after the events of Sonic 3 & Knuckles and takes place before the events of "Sonic Adventure". After Sonic manages to destroy Doctor Eggman's space station, he decides it is time to take a much deserved break. After parting with his companions Tails and Knuckles, Sonic sets off to explore new territories alone.
However, unbeknownst to him, his nemesis, Dr. Eggman, has survived their last encounter, and has revisited and improved some of his very best robotic creations in another attempt to defeat Sonic. Sonic must travel through a variety of zones to defeat Dr. Eggman once again.
The first episode sees Sonic travelling through four main zones: Splash Hill, Casino Street, Lost Labyrinth and Mad Gear, where he battles Dr. Eggman and altered versions of his past contraptions. Upon handling Dr. Eggman's four initial mechanisms, Sonic then squares off against the doctor in a boss battle marathon. If the game is finished with all seven Chaos Emeralds collected, a post-credits cutscene is shown, teasing the appearance of Metal Sonic in the next episode.
Episode II primarily focuses on Sonic's rivalry with Metal Sonic, following on from their last encounter during the events of Sonic CD. Tails also joins Sonic in this episode. Eggman uses Metal to keep Sonic at bay while his plan gets put into motion, which is a new Death Egg.
The game intends to replicate the feel of 16-bit era Sonic games with elements such as side scrolling levels and classic-style badniks. Sonic is the only playable character. Each zone features 3 acts, similar to Sonic 1's design, along with a boss act. The Homing Attack and Spin Dash are present. Monitors return in this game, and power-ups attainable from them include the Speed Shoes, Shield, and Invincibility. Special Stages are present and take place in Sonic 1-esque levels which must be navigated by tilting the level with either the D-Pad or through motion controls on supported systems. If all 7 Chaos Emeralds are collected in the Special Stage and 50 or more rings are collected the player will be able to transform into Super Sonic, a feature which has not been implemented in regular levels in an action Sonic game since Sonic 3 and Knuckles. The transformation is activated by pressing a button that is not Jump, making transforming into Super Sonic less likely to be accidental. In the Wii version, it's simply the button, while on the 360 it is the / buttons.
One controversial issue is with Sonic's design, which uses the modern style model that debuted in Sonic Adventure and has since received refinements until its most recent state in Sonic Unleashed. Many fans say that the classic Sonic design should have been used, and a petition was set up for SEGA to include a classic model. However, in a magazine Takashi Iizuka said that the classic style wasn't returning, as all games since Sonic Adventure have featured Sonic in his modern design. However, this was proven false with the PS3/360/3DS/PC game Sonic Generations, where the Classic style of Sonic was used again along side his Modern counterpart. It is unknown whether this occurrence will be strictly for this new title, or if he will be used in future games.