A good sequel, but way too overrated.
Graphics look great, however there is a lot of collision bugs in the game. You will very often see corpses across a wall, treasure chests that shine even if you already got them and so on. I also experienced 2 crashes. Thanks to the saving system, I only needed to restart the game and I did not lose much of my progression in the game.
Sound is also very good, it is most of the time stable, except in some rare occasions.
The controls still lacks something. When you want to hurry up, Ezio tends to hide in everything he can even if you need to chase someone. When you climb up/down ladders, you need to take your time because Ezio seems to like them a lot. He wants to get back on the ladder when he is done with it. These are all little things that makes the chasing more difficult than it is in fact.
If you want to find everything in the game, be prepared, there is a lot of stuff. There are the feathers, Templar flags, treasure chests. You can also restore the various merchants stands (stable, blacksmith, etc...). You also need to destroy the Borgia towers in order to be able to restore these buildings. However, by completing all of these things, you will earn nothing much than some achievements. There is only the "truth" that gives you a little something when you complete it.
They also added the fact that you can recruit assassins to do some little jobs that give you some cash and objects. However, once again, that does not give you much. You will do some and after a certain time, when your assassins will be "maxed", you will just want to continue the story, because it is great compared to these little jobs.
There is also a multiplayer part, in which you can play as a doctor, mercenary, courtesan or a thief. You need to assassinate someone while you personally are also being targeted by someone. Apparently it is fun for some time, but you get tired of this after a while. I did not try it though. That is still nice that it was added to the game, even if most of the people play more AC for the solo campaign than for the multiplayer.
Globally, that's a good game for action fans, but with his weaknesses. If you are not a fan of the series and want to start with an Assassin's Creed game, this is your bet since it sums up the previous games right at the beginning. However, you would probably be better to wait for it to be on sale on Steam or similar sites, it is frequently on for 5$ only. For the fans, you probably already played it, if not, what are you waiting?