A lot of people justly did not like the original Assassin's Creed. Its painstaking repetition, stiff controls and clumsy combat made for an often frustrating game, and while I agreed with those points, the story alone made it enough to keep me playing.
Assassin's Creed II came out and improved on many of the gameplay elements. Scaling the environment was much smoother and offered more freedom, combat was smoother and easier (though still pretty frustrating) and the story was better than ever. Yet, for some reason I saw a lot of people still reject the game. Maybe they couldn't make it past the slow start of the game, or maybe they still had the first game's impression stuck in their head.
Assassin's Creed: Brotherhood has come along and steps up to the challenge of changing everybody's opinion on the franchise. While die-hard fans like myself were excited to see that it wasn't just a multiplayer-heavy title (Ubisoft did a poor job at advertising it as anything but), I also saw a lot of previous naysayers starting to show interest in the game.
Then the game came out and completely redeemed any bad qualities its predecessors had. Free-running is so incredibly smooth and limitless, many broken things were fixed, and a lot of things that weren't necessarily broken were improved vastly. The combat is so much smoother and makes fighting a large group of people simple, even though at times this may make it seem like stealth is trivial when you could face a few dozen guards and come out literally without a scratch on you. Luckily, the game tends to push you in the direction of stealth to get the job done.
I wish I could write more but the character limit is starting to shrink pretty quickly. But I will say that the Assassin's Guild is an amazing feature, the story was intense, and the multiplayer could use some tweaking for fairness but otherwise is the dictionary definition of innovation. Assassin's Creed: Brotherhood is a must-have game.