Guitar Controller
Guitar Hero III features a newly designed wireless guitar, with the Wiimote sliding into the controller in the Wii version. The Xbox 360, Wii, and PS3 versions will feature a guitar shaped like a Gibson Les Paul, with the PS2 version coming with a Kramer Pacer styled controller. The basic inputs on the controller are the same: 5 fret buttons, and a strum bar, but some minor alterations have been made to make the start and select buttons larger. The controller also comes with stickers to customize your guitar to your personal taste.
Songs
Guitar Hero III: Legends of Rock features 71 playable songs, with 46 coming as "main setlist", and 25 as bonus tracks. 51 of the songs available in the game are master recordings. Guitar Hero III features the most available songs in the series, while also maintaining song download functionality. See Wikipedia's list of songs for a comprehensive look at all the tracks available in the game.
Gameplay
The gameplay of Guitar Hero III is very much the same as in Guitar Hero II, with the addition of several new game modes including online multiplayer, battle mode, and a co-op career option. The battle mode pits one player against another in which they use accumulated star power to send attacks to their opponent, trying to trip them up.
Differences between versions
While the core of the game is the same for all the different platforms, some of the versions feature subtle differences. All three new guitar models are wireless with each having their own unique implementation. The 360 Guitar uses the Xbox's built in wireless controller capabilities, while the PS3 guitar requires the use of a USB dongle. The Wii guitar makes you plug the Wiimote directly into the Guitar's body, which adds extra exclusive abilities such as rumble support, and "twang" sounds emanating directly from the Wiimote's speaker.
All versions of the game have online play where you can shred songs with another player, however the Wii version does not have support for downloadable content. In the future Activision plans to make new songs available for download, as seen with the Xbox 360 version of Guitar Hero 2.
Availability
Console versions were release in the United States on October 28th, 2007 with PC & Mac versions to be release on November 12th. Guitar Hero III wireless bundle retails $100, $100, and $90 for the Xbox 360, PS3, and Wii respectively.