"Rock Band 2 is a music video game developed by Harmonix Music Systems. It is the sequel to Rock Band and is the second title in the series. The game allows up to four players to simulate the performance of popular songs by playing with controllers modeled after musical instruments. Players can play the lead guitar, bass guitar, and drums parts to songs with "instrument controllers", as well as sing through a USB microphone. Players are scored on their ability to match scrolling musical "notes" while playing instruments, or by their ability to match the singer's pitch on vocals.
Rock Band 2 features improved drum and guitar controllers, while supporting older controllers, as well. New features include a "Drum Trainer" mode, a "Battle of the Bands" mode, online capabilities for "World Tour" mode, and merchandising opportunities for the players' virtual bands. In addition to the 84 songs included on the game disc and 20 free downloadable songs, over 1000 additional downloadable songs have been released for the Xbox 360, Wii, and PlayStation 3 versions, with more added each week."
Source: Wikipedia, "Rock_band_2," available under the CC-BY-SA License.