Assassin's Creed Brotherhood is one of the best games ever created in the history of the universe and it is a shame more people on 2o2p don't play it. At least it doesn't seem like many people play it. It should be up there with all the must-buy games. I think it might even be my game of the year, which is saying something considering how much I loved Reach and Red Dead Redemption.
Brotherhood even links with this cool Facebook game called Project Legacy that is kind of like Mafia Wars. I recruit assassin's in the xbox game and can send them on missions to level them there, but I can also assign xp to them every 4 hours through the facebook game. And I can also level them with missions through the facebook game. I'm building an badass guild of assassin's that will come and help me in the xbox game with a press of a button. There's other stuff I can unlock in both games by playing them too.
There is so much to do in Brotherhood it is mind-blowing. And I haven't even tried the multiplayer yet, I've been too addicted to the single player.
The combat is infinitely improved over AC2, but even in AC2 I thought it was fun.
I'm probably going to write a more thorough review once I try the multiplayer, but seriously, everyone should play this game. At the very least, if you can find a cheap copy of AC2, buy it, fall in love with it, beat the crap out of it, and then move straight into Brotherhood. You won't regret it.
It would help to play AC1 before AC2 to know the story a little better, but AC1 is repetitive as hell and kind of a slog to get through. I thought it was kinda fun, but compared to AC2 and Brotherhood, AC1 is pong. Maybe just read an AC1 wiki entry or watch some youtube vids to catch up on the story. But then play AC2. And then Brotherhood. You will thank me.