"You can think of the game as the ultimate collector's edition," Rovio EVP of Games Petri Järvilehto told IGN. "There are new cinematics, extras and other entertaining content. In addition all of the existing material has been uprezzed and re-treated for the high-resolution and big screen." New "reactive" backgrounds take advantage of the fact that you're playing on a screen big enough to see backgrounds.
The upgrades also feature Kinect and Move capability, as well as StreetPass functionality on 3DS. Most importantly, they support the "being able to be bought and given as holiday gifts" functionality that Rovio has lacked so far.