I'm a big fan of Assassin's Creed. The mysterious lore is so engaging that it's hard not to speculate. And I've spent over thirty hours playing the game, so I can give a valid review.
Most reviews I saw gave it a 9 or 8 and this is well-deserved. This game is basically the AC2 template set in Rome, and a weaker story. Although the story I don't blame them for since this is an offshoot of the franchise and an ending to Ezio's story, not a numerical release. Just make sure if you plan to get this game, play the first two so you aren't completely lost. Also, be prepared for a WTF ending (we've come to expect this from the series, but really, it gets me every time I see it).
Graphically, this game is a slight improvement to two. This is the most impressive feat the game achieves because when strolling through the streets of Rome or galloping on horseback (a welcome addition that adds to the realism) you really feel like you are in 16th century Italy. The view is breathtaking from any high ledge and Ubisoft does a particularly amazing job making it all seem real. People act like actual people and the voice acting is spot-on (lead by the growing annoying presence of Nolan North as Desmond). They gave the player all the liberties expected and this game fulfills the duty of truly being called "open world".
One thing that will keep people playing until next year's release is the sheer amount of stuff to do. It seems everyone is in need of an assassin. Courtesans, thieves, mercenaries and regular citizens all enlist Ezio's help in side missions. The ones I like best are the assassinations of Templar agents around Rome. There is also businesses to buy and operate, historic landmarks to purchase, and flags and feathers to collect. (Flags are limited to only 100 across Rome and there's only ten feathers, hallelujah).
The reason the game is called "Brotherhood" is that Ezio's main mission through the game is to reestablish the Assassin Brotherhood. In doing this, a brilliantly addictive metagame was implemented. The player can send his assassins all over the existing world, from Constantinople to Cologne, to complete contracts for florins (the currency) and items used to complete shop quests. There is a consequence to this: Ezio loses the ability to call his assassins in combat. Your assassins can be called in combat and tough spots in missions to ease the difficulty. And, oddly enough, they are better assassins than Ezio.
My favourite mode of this game, and I hope everyone else's, is the multiplayer. Basically, it's kill or be killed. The best way to describe it would be thrillingly frustrating. Every person walking could be out to get you, and when you make a mistake, it will cost you. Luck does play a big factor, though, so don't get too mad if you don't have a horseshoe up your ass.
The Assassin's Creed franchise has done something rarely happening these days: created a truly compelling world gamers can test their intuitive chops figuring out. This series has captivated audiences with its lore and inventive gameplay. I hope this time next year I'll be singing the same tune.