The latest information on Rock Band 2 comes to us from the that spot for games. First, let me introduce the first set of confirmed songs in Rock Band 2.
"Ace of Spades" -- Motörhead
"Everlong" -- Foo Fighters
"Pinball Wizard" -- The Who
"Panic Attack" -- Dream Theater
"Any Way You Want It" -- Journey
"Chop Suey" -- System of a Down
"Kids in America" -- The Muffs
"Give It Away" -- Red Hot Chili Peppers
"Hello There" -- Cheap Trick
"Pump It Up" -- Elvis Costello

Now, here is a list of features in Rock Band 2.

- Online Band World Tour
- Quickplay Setlists
- "Battle Of The Bands" Mode
- Band Challenges replacing Solo Tour (Essentially Solo BWT from the sound of it. DLC integrates with Band Challenge.)
- No more band leaders and any character can play any instrument
- You can now hire staff
- New guitar will autocalibrate, sturdier strum bar, wireless out of the box.
- New drums are velocity sensitive, less noisy, also wireless.
- "because the game will feature full support for all of the original Rock Band songs"(this quote has now been edited out of the original article)

Band Challenges will be specific challenges dedicated to the instrument path that you decide to take with your character. There will also be challenges based on your DLC. One example of this is you can do a challenge based off of the Pixies album.

This quote explains the Battle of the Band feature very well.

"Harmonix will be creating new daily battles for bands to take part in; some will even have unique entry requirements, or gameplay modifiers. When playing Battle of the Bands challenges, you'll see an onscreen score, along with a score that you need to beat (such as someone on your friends list who has also competed in this challenge)."



So, who wants to join my band for some OBWT?

Source