Lets face it: Gameplay-wise the "The Beatles: Rock Band" isn't a huge departure from, say, "Rock Band 2." Apart from 3-part harmony and some new training modes, you're going to have a similar experience in the actual playing of it. But Harmonix is definitely trying to make this feel like a unique and very "Beatles" experience, so they've redesigned the game's story mode specifically for hardcore fans.
The story mode is broken up into venues taken from the Beatles history. From the Cavern Club to Shea Stadium to the rooftop of the Apple Corps. building. Each venue has songs taken from the time period, and depending on how well you do on those songs you'll earn stars (again, a carry over from "Rock Band"). Earn enough stars and you'll unlock photos and factoids from the span of The Beatles career.
Earn 9 photos and you'll earn "other media" from The Beatles career. The example Harmonix was showing off was the full audio from the original Beatles Christmas album. It's this strange time capsule where The Beatles are all just sorta screwing around on tape. It honestly sounds like the progenitor of the podcast, but with one of the biggest bands of all time.
Audio and video will make up the bulk of this "other media," and a lot of it was dug up from the archives at Apple Corp. Paul McCartney even offered anecdotes and insight on certain events, confirming or denying facts that have long been rumored but never really confirmed.
So really, if you're a Beatles nerd, you're probably going to obsess over the story mode. Don't say I didn't warn you.