Well, Destructoid dug up a page on xbox.com that offers some additional details, and it sounds like there will be a lot of weird stuff going on around you while you play your plastic instruments. What kind of weird stuff, you ask? How about destroying robots and skyscrapers with the cleansing power of rock?
Also, like the other Lego games, it sounds like you'll earn bricks as you play, which will let you build bigger vehicles... this sounds like it'll be part of the game's progression, so instead of earning a jet by building fans and stars, maybe you'll just earn enough bricks to build a jet and then travel on.
Here's the rest of the story from the xbox.com page:
- Songs you know and love: Rock out to everything from current radio hits to past favorites the whole family will enjoy.
- LEGO-themed rock challenges: Play killer riffs to destroy a giant robot, summon a storm, and demolish a skyscraper using the power of rock!
- Enhanced customizer: Don't stop with your avatar, customize your whole entourage! Design the band, roadies, and manager just the way you want.
- Build fame LEGO-style: Collect LEGO bricks after each song to build cooler vehicles and move to new venues.
- LEGO rock den: Buy furniture, decorate the walls and customize your band's hang-out as you climb the ladder to rock success.
- Fun for everyone: Turn down the difficulty with an easier skill set option for budding musicians.
With an easier difficulty and its Lego focus, it's easy to see that this is designed to be a bit more family friendly than the other Rock Band games. But if it supports songs from Rock Band, Rock Band 2 (which will probably have to get a song export option sooner or later), and the existing downloadable content, I'd probably pop this disc in instead of Rock Band 2, just to watch Lego dudes hopping around in the background. Though now that I think about it, I can't remember the last time I actually popped in a copy of Rock Band 2, either.