Gamers Temple: "While Super Sonic is chasing Eggman in what appears to be their final battle, Eggman manages to trap Sonic and the Chaos Emeralds. By firing a beam of reverse polarity Chaos Emerald energy at the planet, an evil being known as Dark Gaia is released from the planet's core through Eggman's scheme. While being trapped along with the Chaos Emerald's reverse polarity while the shot is fired, Sonic is now transformed into a Werehog at night. In order to restore the planet, Sonic must journey throughout the world and restore power to the Chaos Emeralds once again in order to bring the planet back together and stop the threat of Dark Gaia.
There are two stage types in Sonic Unleashed: Day stages and Night stages. Day Stages allow you to play with the normal blue Sonic the Hedgehog and these stages have a very traditional Sonic feel to them. The stages are showcased in full 3-D with a back view of Sonic as you race forward through the many obstacles. The sense of speed is showcased well as Sonic zips down a runway and, much like previous Sonic games, you can sort of let the game play itself as Sonic runs - up to a certain point of course. There are hardly any barriers that keep your Sonic from dashing frantically through the various levels. The game still sometimes switches the camera to the side of Sonic to showcase a side camera view that resembles a 2-D view reminiscent of the older Sega Genesis Sonic games."