The physics puzzle is what attracts most people to the game. But I've noticed with my son the "story" elements, sounds, and characters are also a big draw. He actually wanted an angry birds stuffed animal for Xmas, after seeing the ads on the mobile game.

In addition, for my son I've found that the physics element in Angry Birds has helped build interest in other physics puzzles, including those that don't have as much flavor, such as Ragdoll Blaster.