Just because a trailer is entirely CGI doesn't mean it can't tip off clues to gameplay features and story arc.
Sure, there are gameplay trailers out there, coming from E3. But Gametrailers' breakdown of what you can expect to do in the game - likely done with Ubisoft's assistance - is nonetheless a thorough and enjoyable look at the targets of Assassin's Creed 2, how you'll eliminate them, who will help you, and where you'll pull off the jobs. It's a great way for those of a casual interest to get up to speed with a sure-fire blockbuster.
Assassin's Creed II GT Pop-Block: Venice [Gametrailers]