In an interview with Sega Saturn Magazine, Sega's Yuji Naka talked a little bit about the upcoming Dreamcast Sonic game, Sonic Adventure. According to Naka, Sonic Adventure was initially called Sonic RPG. Even though the game's main focus is action, there will obviously be more to it than just that.
As you've probably seen, currently there is only one piece of artwork available for Sonic Adventure. It only shows Sonic's mysteriously green eye and a big grin. According to Naka, Sonic's design will change a bit this time. We'll see the new Sonic when Sonic Adventure is officially unveiled on August 22.