There are a few new wrinkles. Sonic has his homing attack from Sonic Adventure, for example. As with most of the 2D Sonic titles, there are also a few interesting locomotion mechanics sprinkled throughout the levels: vines to swing on, ziplines and, of course, the beloved corkscrews and loops.
The homing attack adds a new layer to the traditional flow of Sonic games. For example, there are many moments throughout the first levels when Sonic will be launched into the air and then be able to smash a string of enemies using the homing attack. If you do this successfully, you can access higher areas of the level. If not, you'll fall down and take a different branch. Which reminds me, the levels have retained the same branching pathways that made exploration enjoyable in the original titles.
I was told that the final game will have a total of four zones, each with three acts and an Eggman boss fight. In addition to the normal levels, there are seven special stages -- I wasn't given details on how those will work, incidentally. And yes, Super Sonic will be available if you managed to snag all seven Chaos Emeralds. Collecting all the emeralds will also unlock a cliffhanger ending that leads into the next episode.
The price still hasn't been announced, though I was told it should be appropriate for the length of the game. As to how many episodes there will be, the rep informed me that Sega has no intention of stringing out a huge number of episodes and gouging consumers for more cash. According to the rep, there will be a "very finite" number of episodes.
Based on what I played, Sonic the Hedgehog 4 should be exactly what fans have been craving for years. It's not surprising, given what co-developer Dimps has done with Sonic on the DS in the past. The only difference is that now it's available on a console. So, if you've been waiting for some pure Sonic action, Sonic the Hedgehog 4 - Episode One looks like just the ticket.