The Sonic series has been pretty notorious for being an underwhelming series. With Sonic 4, it seems that Sonic is taking a turn back to its traditional roots that everyone had come to love. Then again, Sonic 4 isn't being worked on by the Sonic Team. The Sonic Team is, however, working on a new title exclusive to the Wii and DS, titled Sonic Colors.
According to the Sega Blog, Sonic Colors will maintain the high-speed oriented gameplay that is familiar with the Sonic series, but sonic will be racing his way through very colourful, theme-park inspired levels with alien wisps that give Sonic "Color Power" to activate abilities such as drills and lasers.
Sega also released a teaser trailer, and though it doesn't show much, it does show the little alien wisp things moving about throwing colour all over the place. Hopefully the Sonic Team can pull something together, though given their tack record, there is reason to worry.
Source: Sega Blog