I'm enjoying Assassin's Creed 2 for the PC. There are so many improvements made compared to the first game. You can use different weapons now, have more various killing moves and new assassination techniques (it's pretty awesome to stab n throw a guard off a roof while hanging just under him or stab a guard from inside a haystack and pull him in).
There's a new economic system in place too. You actually have money and can upgrade your town with it which in turn brings in more money. A lot of people complain that the economy system is pointless but I'm not one of them. The main point of the game is to kill people. I find the economy mini-game is a nice little distraction.