You'll get completely burned out on Assassin's Creed if you try to play the other games first, unless you're planning on spreading them out and not playing this game until 2014. They're pretty long games. :p
I think you'll get the gist of the main story pretty easily, so you'll only be missing out on the details, and they're a convoluted mess at this point, anyway. Assassins: good guys. Templars: bad guys. Apples of Eden: MacGuffins. That's all you need to know, and I'm sure the game tells you as much in the intro. I say you should just dive right in!