Gameplay
To further the traditional "Sonic formula", every level was designed in a tube-like fashion; Sonic would be able to walk onto walls, thus changing the direction of gravity and the rotation of the level itself, much like the special stages in Knuckles' Chaotix. In addition, an unusual, fish-eye lens-styled camera was put into place so players could see more of their surroundings at any given time.
At one point in the development process, there was a possibility for 4 playable characters: Knuckles the Echidna, Tiara Boobowski, Miles "Tails" Prower, and Sonic the Hedgehog, with each character having a unique gameplay style. Knuckles and Tiara would have had traditional-style play, having top-down and side-scrolling views respectively. Sonic had the fish-eye style levels, and Tails would play in first person flight mode. Tiara had the Ice Blade to fight her enemies. Sonic himself was to be equipped with a large set of new moves, including a "spin slash", a ring throwing ability, and a downward dash.
Other characters intended to be included in the game were Nack the Weasel and Metal Sonic, who would have been a boss character in the final level.
There were six planned Zones: Jade Gully, Crystal Frost, Red Sands, Blue Ocean, Metal Blade and Galaxy Fortress.
Read more about this topic: Sonic X-treme