Here's a link to
my full review of Assassin's Creed 1.
I gave it a B. It's a decent game. If you really want the full story experience you can go ahead and play it, but all the game elements of AC1 are present and/or improved upon in AC2. While you might be missing out on some backstory if you just jumped right to 2, I don't think it would be otherwise harmful to the gaming experience... IE, you don't need AC1 to play AC2 well.