When something is larger-than-life, it seems more important or fascinating than anything else around it. An actor who is mild mannered and shy in person can seem larger-than-life when she's on the stage.
You can use this term for something that's actually larger than usual, like Michelangelo's larger-than-life statue "David," which is three times as tall as the average man. It's also a good way to describe someone who is so flashy and flamboyant that they just seem to take up extra room: "My larger-than-life cousin makes every family gathering much more interesting."