This info comes from the latest issue of Official XBox Magazine UK (courtesy of GoNintendo):

- back to basics approach
- past Guitar Hero characters return
- recruit each character by playing their song sets
- unlock their alter-ego and gimmick (Lars becomes Warrior Lars, and allows you to get a x6 multiplier)
- quickplay feature revamped
- carry over previous DLC
- Streakers, Momentum, Do or Die now available in online competitive modes
- new Power Challengers
- Queen, Kiss, Black Sabbath confirmed
- Quest Mode features Gene Simmons as narrator
- sustain open notes when playing bass
- CBGB is the only real-world location to appear
- no real-world celebrities as playable characters
- much bigger focus on rock 'n' roll

http://gonintendo.com/viewstory.php?id=123689

Being one of the apparently few who actually enjoyed Guitar Hero 5, I'm looking forward to this one.

But from what I read in the OXM article, the character morphing alter-ego's gimmick sounds pretty outlandish and unnecessary. Like the way Lars can turn into a warthog...