Having played the first Assassin's Creed on release day as well, which was a good game but it missed a good story and depth. Assassin's Creed 2 on the other hand has been beaten and moulded into perfection.
There's alot of small things about this game that are done so well as well, but I'll start with the big stuff. The world is huge and the environments are so detailed. The story is very deep and by the end you really feel really connected to the Character you play Ezio. One of the main things I love about this game, is theres alot more variety in missions and also in combat. Combat now has several different ways to take down targets and also escape methods which are really handy when your surrounded or you just cannot be bothered to fight. This game also has an economy system, which works around you getting money from missions and then using that money to upgrade items or your villa, which increases the value of the villa and thats gives you more money.
This game will keep you constantly entertained and I can tell you, you will not get bored while playing through this game. Its very difficult to put down and not only that but its pretty long as well, especially compared to the first one.They really have done a fantastic job of the sequel, everything has been made better and after seeing the end I'm really looking forward to the next one.
I'm gonna have to give this a 10/10, because I can't really fault it on the single player experience and although it has no multiplayer, I don't know how they could incorporate a multiplayer into it (maybe the next one :) ).