To start, the game is built on an entirely new engine dubbed the "Hedgehog Engine." Don't let the totally clever name fool you; despite being built for Sonic's specific needs – ie: it loads art and whatnot very quick – it's a multipurpose engine, and it's been in development since 2005. How is a fancy new engine going to bring Sonic into the modern world of games? By going back to its roots.
The two levels Sega shared were definitely fast. In the first level, Sonic zipped through some six miles of terrain in roughly 3-1/2 minutes. The levels included Sonic hallmarks like split paths – about 15 in this particular. Some splits involve a button press quick-time event (hit the right buttons, get the better path) while others were simply left or right, up or down. New moves include the Sonic Drift which, you can surmise, is similar to drift racing, slinging Sonic around hairpin curves. The other is Quick Step – instead of running straight into a wall, or an enemy, or laser beams (you get the idea), Sonic can quickly jump left or right by tapping the controller's bumpers.
If you've seen the trailer, you've already seen the split between "2D" and 3D gameplay which is admittedly pretty seamless thanks to a solid camera system. The presentation certainly emphasized the game's speed, making it feel like a classic Sonic side scroller. While that's bad news for fans of Sonic's Dreamcast adventures (and the rep did say there was no "real" adventure element), there will be an "optional" overworld. Nevertheless, with an entirely separate "combat fighting" mechanic (as opposed to that other type of fighting) making up the nighttime half, we're as skeptical as ever of this latest attempt to reboot the popular mascot's flagship series. We'll know more at E3. Probably.