Just like in Assassin's Creed 1 there are cool mechanics here but ultimately falls short.
(Warning, there will be spoilers from AC1 and AC2, those that have not played the previous games stop reading here...)
Brotherhood takes place right after the events of the second game staring Ezio Auditore da Firenze confused and bewildered after witnessing the hologram of Minerva warning of a major catastrophe to happen in 2012. Due to circumstances of the second game it leads an attack against the villa and the Apple of Eden falls into the hands of Cesare Borgia which is your main target for assassination throughout the game, as well as anyone connected to him.
Alongside this there are also a few side missions that are not required in order to progress through the game but it will make up for the short campaign if you do. The side missions require you to destroying 4 war machines designed by Leonardo De Vinci, synchronizing 24 view-points, several chambers similar to AC2's Assassin tombs, and lastly a few random quests here and there that can be done by your fellow assassin recruits.
For the most part the story is weak, I feel it to be an excuse to keep us away from Desmond and the events that are happening in present day, the entire reason for all the trouble with the animus is just to retrieve the Apple of Eden which we already knew from the first game. As well there are many times in the single player where missions are dragged out alot longer than they should be (following a target for 15 minutes makes me wonder if it is just to make up for the short story).
The biggest additions to the game such as the inclusion of other assassins and being able to utilize them in battle comes off as shallow. You destroy Borgia tower which then allows you to save and recruit a new assassin, though it never goes any deeper than that. You send them on missions all across Europe but never get any real details as to what they're doing nor do you get any sort of reward from doing them. They are also not implemented into the actual story either, you can go through the entire game without ever using one of your recruits making them come across as just another weapon in Ezio's inventory.
I could go on about how being in one city no matter how big it is gets old or looks like a step down compared to AC1/2 that offered 3 to travel to, and how restoring Rome doesn't make much of a difference but I'll finish up
The MP is fun, it is fresh and unique though there are a few annoyances that can be patched up, and hopefully there will be downloadable content.
Graphics are still beautfile
The combat is better though that is because you don't have to play the waiting game with your opponent.
Its truly not a terrible game but I feel just like in AC1 there were some great ideas that can be better polished and defined in a sequel.