Sonic Robo Blast 2 is a free 3D Sonic the Hedgehog fan-game built off a heavily modified version of the Doom Legacy engine. It is closely inspired by the original Sonic games from the Sega Genesis, aiming to recreate their classic gameplay in a 3D environment while also providing a full host of multiplayer modes and features in a fast-paced mix of FPS and platforming gameplay.
Here's a clip montage of what you can expect from SRB2's single player campaign. Please excuse the lack of sound; we hope the music compilation (which is from SRB2) makes up for it.
Enjoy! Be sure to look for Part 2: Multiplayer soon!