Here's the alleged information. Guitar Hero IV features the requisite Rock Band features: drums, vocals, bass, guitar and create-a-rocker. Additionally (and most interestingly), there will be the option to create your own song tracks. Although vocals are excluded, all other tracks can be made and uploaded to GH Tunes for sharing and rating. We're not sure how this will apply to songs not in the game, given copyright concerns, but color us intrigued.
All songs will reportedly be master tracks, and four bands have been confirmed: Van Halen, Eagles, Linking Park and Van Halen. Is this the "significant leap" mentioned by Activision last week? Until we can obtain a copy to verify, consider this a rumor.
