It's not often that you come to the third game in a series and have it called a great place for newcomers to begin playing the series. In most cases, you'll want to play the games leading up to the newest release in order to follow the story. With the sometimes convoluted nature of the narrative in the Assassin's Creed games, you'd think that this would be the case here as well.
But not so! According to Rob Cooper of Ubisoft, "This is a great time for gamers to join the adventure. There's a huge will from Ubisoft to bring more gamers into this universe." So if you've been living under a rock and somehow managed to miss out on the previous four Assassin's Creed games, you can still jump in here and have a good time. And since Assassin's Creed 3 seems to have the coolest setting and protagonist we've seen so far, that'll be good news for people who want to jump in here.
Mr. Cooper went on to say "Assassin's Creed III is the biggest and most ambitious launch in Ubisoft's history, so we absolutely believe this game will continue to grow the franchise." Based on the information we've heard about the game so far, I'd say he's probably right.