Playing Assassin's Creed Brotherhood is an enjoyable experience, but it does not leave you satisfied.
The missions in brotherhood are very varied and fun, there are also various flashback missions with Cristina(Ezio's girlfriend from AC2). In each mission there are 2 objectives, the first, is the main objective: To complete the mission and kill the enemies, etc, the secondary objective will be harder, and will be along the lines of 'don't go into water' or 'don't get caught once'. This adds a bit of replay value, especially as increased 'sync'(50% if you completed the primary objective, 100% if you completed both) unlocks other things, such as Cristina's flashback missions.
Although I enjoyed playing through the single player of brotherhood I felt that it was very short and brief, I finished the single player in a little over a week; playing through missions again to complete the secondary objectives is enjoyable at first, but quickly becomes a frustration on some missions. As well as this, once you complete the missions, you are left with little to do, again like AC2.
In AC:B you are able to control and mentor Assassins, where you can send them off to missions across Europe and aid you in combat, they can also die, and you have the option to 'close there eyes' which is interesting. While this is fun to experiment with the first time, Ultimately it is just a gimmick and isn't very useful, especially as Ezio is now as powerful as a one man army.
Certain Items require challenges to be completed before you could buy them, this requires you to find items to complete the challenge. I played through the entire SP and only found 4 Vlad the Impaler coins and found it boring to find chests to recieve more, so I never completed these side quests. I did, however, complete all the lairs to unlock the 'ultimate outfit', which behaves like Altairs Outfit in AC2: it gives maximum health and is unbreakable.
Playing through these lairs are very fun and challenging, I myself failed one or two times before persevering and moving on.
Combat is even easier than AC2, in brotherhood, you can perform insta-kill combos, where if you achieve an instant kill on one enemy, you can quickly perform it on the others in a chain which is very useful when fighting Brutes. This also makes combat very easy and it is simply: Wait for the right moment to execute an insta-kill, then combo kill the others.
The reason I gave this game a rating of 'easy' and not 'very easy' is because the Lairs and Secondary objectives add a option of difficulty.
As well as the single player, you have a multiplayer which consists of 2 modes:
Wanted - You have to blend in and find a target, and then kill them for points - a quick tip is to not run and them to get the most points.
Advanced Wanted - Same as the above but you are given less information on your target
Manhunt: One team hides, the other pursues and attempts to find and kill them.
Alliance: Basically the same as manhunt, but with 6 players divided into 3 teams.
AC: B multiplayer is very enjoyable and addicting and I recommend that you try to play it after you have playing the Single player.
Overall Assassins Creed: Brotherhood is an enjoyable experience that is very fun and pretty, but it could be improved upon and given a more satisfying ending.