“As we’re spending more and more time with digital products, UI is becoming one of the most important areas of design, but it’s also one of the trickiest to judge. When user interface design is good, it’s hassle-free and we don’t have to think about it; but when it’s bad, it can make our lives hell. […]
Digital devices have become progressively more complex. Making them easy to use has become more difficult for their designers, and even more important to their users â€” as everyone who’s had to struggle with an over-complicated cellphone knows to his or her cost.”
The article goes on to describe fun and sensuality as important factors in good interface design.