Some more details are in Game Informer this month, so pick up your copy. The biggest complaint about the first one is how it can be painfully repetitive. Also, the enemies are better and smarter. You don't die the second you touch water like Sonic the Hedgehog. Ezio is the main character in this one too.
Here's a link to ign's article and a trailer: http://xbox360.ign.com/articles/973/973234p1.html
You guys looking forward to this game or what?