Sonic Generations for the 3DS is not the same game that will be released on the PlayStation 3 and Xbox 360. The 3DS game features stages that are based on the classic early 90s games along with stages that play similar to those in the Sonic Rush titles.

The demo at E3 only featured two stages in Green Hill Zone and a boss battle. The classic music always puts a smile on my face and while it was hard to hear because of the noise of E3 it still got me in the mood for Sonic. The first act lets you play as the classic Sonic who has his trusty Spin Dash move. The Act 1 stage design hewed closely to the Genesis classic with some slow platforming moments along with the plenty of loops and familiar Badniks like Crabmeat and Buzz Bomber. 

The second act was a modern Sonic level, which visually looked pretty much just like the first. Modern Sonic does not have the Spin Dash move, and instead has a dash activated by Y and the homing attack. While the action always stayed on a 2D plane, the camera did sometimes slightly tilt sideways and there were grinding rails and other more modern elements.

The boss battle took place in a circular arena with a classic Robotnik form that was originally seen at the very end of Sonic the Hedgehog 3. Robotnik even had some of his attack patterns from the old Sonic game.

Green Hill Zone in many ways was always destined to be seen in 3D with the original Genesis title featuring many different background elements like waterfalls.The 3D effect worked really well especially when Sonic was going through a corkscrew. In the modern Sonic level, it was necessary at one point to dash through the bottom of a giant totem pole. Once I had broken through the bottom, the rest of the totem quickly fell towards the running Sonic who just barely escaped being crushed. The totem falling looks great in 3D and is just one of the many great uses of the effect.

The biggest problem with the game was that the framerate was far from smooth. Act 1 featured a lot of slowdown and you honestly can't have a good Sonic game if he isn't moving fast and elegantly. Act 2 seemed to have a better framerate and was the more enjoyable stage because of it.

I'm a big fan of the Genesis Sonic titles and it seems like they the development team is successfully mimicking the old school gameplay and level design. I just hope they improve the frame rate.