Late and out of date, here's my review of possibly the biggest music game ever. The original Rock Band was nothing short of fantastic, but it had some apparent hardware - and software - issues that needed to be addressed. Needless to say, RB2 has fixed most of those issues. 
Rock Band 2 has the same formula of the last iteration for instruments. There's the Lead Guitar, Bass Guitar, Drums, and Vocals. Up to four friends, online or offline, can simultaneously play a song. Of course, you have to play through the "world tour" mode to unlock all of the 80+ tracks available then. You create your rock character, and you (and up to 3 other people) tour across the world playing vast amounts of songs (though sometimes repeating a tad too much). The farther along you go in the tour, the harder the songs get, and sometimes it forces you on certain songs to play on a harder difficulty. You unlock cities, within cities venues, and within venues gigs, to play songs that have been selected. Most cities and venues need you to have a certain amount of "stars" which you get while playing songs, and fans, which you get also while playing songs. Not the best organized, but better than the first game. 
The hardware for Rock Band 2 has been increased in quality as well. Most notably, the drums. Remember how the pedal would easily break? Well, screw that. Harmonix replaced the plastic with much more, sturdy material. The guitar looks sleeker, and even looks less like a toy. Still has the five buttons at the bottom of the fret-board, which, you know, is nice. The mic is relatively unchanged, but hey, how innovative can you get with a mic? All of the original Rock Band peripherals are compatible with Rock Band 2 for the same console. The newly designed peripherals for Rock Band 2 are backwards compatible with the original Rock Band. One of the best parts is, Rock Band 2 works with all official Guitar Hero instruments (and most 3rd party instuments) as well, (and vice versa!) so you don't have to have two drum sets, four guitars, and a couple mics for the music game experience, which is good, because my room can't afford much more equipment crowding it up.
The set list in Rock Band 2 is nothing short of fantastic. Everything from thrash metal to pop rock is here. Megadeth, Paramore, Bon Jovi, The Who, whatever you like, it's probably there. The greatest thing, by far, about Rock Band 2 is the Downloadable Content (DLC). There are hundreds upon hundreds of songs to download at the Rock Band store. Buy full albums, track packs, or individual songs. That expands the set list so far, that if you basically like any kind of music, there will be something for you in the Rock Band store. Plus, if you've already downloaded a bunch of songs from Rock Band 1, it automatically transfers the DLC from it to Rock Band 2, free of charge! Also, you can import your Rock Band 1 (minus a couple) tracks into Rock Band 2, for a small fee (of course).
All in all, this game is a fantastic sequel to one of the most innovative games of this generation. More songs, more features, upgrades to the minor problems over Rock Band 1, there is little to complain about in this epic game.
