According to a NeoGAF poster armed with the latest issue of Game Informer magazine, Guitar Hero IV will, as expected, focus on more than just faux guitar playing, as the next proper iteration is said to add drums and vocals, just like Rock Band. Where GH IV is expected to go above and beyond the Rock Band experience is in its custom creation modes.
Guitar Hero IV will feature a "create a song" mode, allegedly, which appears to let gamers lay down guitar, bass and drum tracks—but no vocals—then upload their creations for others to enjoy. That song sharing mode is said to extend beyond the PlayStation 3 and Xbox 360 versions, with Wii and PlayStation 2 versions getting their own song sharing.
Additional details from the NeoGAF post indicate that players will be able to create custom virtual musicians, virtual guitars and virtual drums. As for the licensed stock tracks, tunes from Van Halen, The Eagles, Linkin Park and Sublime are said to appear.
More early details on Guitar Hero IV at the original post. Expect to see official word in no time at all.
Game Informer June 2008 Issue [NeoGAF]