Sonic Superstars is finally available, and by all accounts, it is a reasonably decent addition to the 2D Sonic franchise. Eurogamer has published a lengthy interview with the head of the Sonic team, Takashi Iizuka, which covers a range of topics. One thing to note from the interview is where the newly released Sonic Superstars fits within the Sonic the Hedgehog video game timeline.
Mr. Iizuka explained that Sonic Superstars is set after the events of Sonic, but before the classic SEGA Dreamcast game, Sonic Adventure.