After teasing an announcement with the release of an all-CG trailer, Sega pulled the veil off of its latest effort to make the Sonic the Hedgehog franchise one you want to love again: "Sonic Generations." With the series hitting its 20th anniversary this year, this upcoming game -- which is set for an unspecified 2011 release -- will be a multi-generational Sonic adventure, bringing in characters from the Genesis era onwards. Today we've got the very first gameplay trailer for you, which you can check out after the jump.

The trailer pulls in footage from the same demos that have been making the rounds in the games reporting community over the past week. Russ got to go hands on with the game, so hit that link to read through his thoughts.

"Sonic Generations" is essentially two games in one, which each level getting 2-D and 3-D treatments. The 2-D isn't strictly two dimensional, as you'll see in the trailer, falling close to last year's "Sonic the Hedgehog 4: Episode 1." The 3-D also isn't strictly over-the-shoulder; the camera changes position dynamically depending on what part of the level you're running through.

Both the previews and the content in this new trailer focus on the game's level set in Green Hill Zone, which first appeared back in 1991 in the original "Sonic the Hedgehog" game. The level layouts are changed for this new game, and also differ depending on whether you're playing the 2-D or 3-D flavor.

Very little has been revealed so far about the story, though Sega has revealed that there is one which justifies bringing all of the various Sonic eras into a single game. The fast-running blue hedgehog and his friends are pulled into some kind of time portal by a mysterious power and there will presumably be some looming great calamity to be set right. More news is coming at E3, so you'll hear all about it soon enough.