i'm really impressed with the sequal so far.
Customization in a game is pretty much my top must haves if you ask me and AC2 pulled it out when it came to letting you make your assassin how you want.
New weapons, new minigame type missions, clothing styles, bigger cities and taller buildings, less obvious and non-bland climbables including TONS MORE climbables(pretty much fucks infamous up the ass) and most awesome part.... armor!
Also the new feature to customize a whole town you have to yourself is great. Reminds me of the ol San Andrea/godfather days. You make money off your town renovate parts of it, getting discounts and all sorts of unlocks.
Again much more impressed with the sequal. In my opinion AC1 was the starting point for the gameplay mechanics and AC2 was the branching out and expansion using their new found mechanic and making something really great.