5. More Than One Storyline
We saw vague shades of this in the original Lego Star Wars with the bonus A New Hope level where you played as Darth Vader and a Stormtrooper but it really didnt come into its own until Lego Batman, which featured fifteen additional levels where you played out the main storyline from the perspective of the villains. As well as the additional content providing better value for money, its just quite a novel feature since its a change from exclusively playing as heroes or villains, which is a common convention in games. Particularly those in the comic book genre. Plus, playing as the villains and wreaking havoc is always much more fun than being the hero and saving the world. Especially if it's an alternate continuity where you can kill some of the characters you're none too fond of.