A game definitely worth playing. Wraps up Ezio's story as well as immersing us in some of Altair's memories. Great game.
In Revelations, the developers added den battles. They were completely pointless and a waste of time. I thought it was cool at first but they occurred so often that it took away from continuing the story. After each den capture, you become notorious and almost within a minute or so a den would be under attack. Like I said above, it was fun the first couple of times, but after that it just became annoying. All I wanted to do was continue the story; however, I had to stop every so often just to do the den battle. Another thing I was disappointed in was the lack of a horse. I really enjoyed using a horse in Brotherhood and was upset it wasn't in Revelations. It definitely made travelling easier. Tunnel entrances were once again in the game but when you need to travel on foot from there, it just wasn't as fast as it would have been with a horse.
Overall, this game is definitely worth playing. Other than the few disappointments I pointed out, it's a great game. I play Assassin's Creed for the single player, not the multiplayer and therefore, I cannot tell you anything about that aspect of the game.