There was a really good article in a issue of Game Informer Magazine. I scanned it so everybody can read it. I didn't wanna re-type it all out so you'll just have to maximize it and scroll left or right/updown to read it.
I thought it was a really informative read. It'll take you awhile but it was worth it. They go over the 10 must-know features to prepare you for the biggest and most complex game yet in the franchise.
10 Things to know before you play Assassin's Creed Brotherhood
Reasons 1 & 2
Reasons 3, 4, and 5
Reasons 6, 7, and 8
Reasons 9 & 10