Designing for the user experience has a lot more to it than making a product usable. Usability allows people to easily accomplish their goals. UX design covers more than that, it’s about giving people a delightful and meaningful experience.
A good design is pleasurable, thoughtfully crafted, makes you happy, and gets you immersed. Think of games, they usually have these characteristics. Or think of the iPhone that makes even failures “more enjoyable than succeeding on a Blackberry”