Assassin's Creed II, first and foremost, is extremely better than the original. Not only is there more to do, you can also buy new weapons, learn new moves FOR those weapons, and change the color of your outfit. For me, those were some of the biggest improvements.
Now, let's talk about gameplay. Assassin's Creed was smooth, well animated, and fast. In the second game, things have changed just a little bit. The basics are still here, and now there are two blades. This time around, you get smoke bombs, a small modification to the blade that can make it a gun, and my favorite, poison. With the poison, you approach your enemies, stick them with the blade, and they become a spectacle for any and all that are around, they take their weapon, and swing it around, if you're lucky, they'll take out some of their buddies, doing the job for you, leaving you to just loot their bodies.
This game is one of the best games I've played this year. In fact, I sacrificed getting Left 4 Dead 2 to buy this game, and frankly, I'm glad. If you have any problems with my review, please do not leave idiotic comments saying how stupid/sucky it is, I'm just here to give you my opinion and my thoughts, but by all means, if you do like this review, please tell me.