One way to explain User Experience Design is to contrast it to Usability.
Usability is about the "ability to use" something. The aim for a usable product is to make it easy to use. A product has a high level of usability when:
• It requires less mental effort to use.
• The frequency of mistakes using it is less, or the mistakes are less disastrous.
• It is more powerful, where "more powerful" means that it can be used to do more or do it faster.
• It is more learnable, that is, when a person can figure it out quicker.
User-experience is not like usability - it is about "feelings." The aim here is to create happiness. You want people to feel happy before, during and after they have used your product. To do that you need to take all kinds of things into consideration. Things like:
• Colors moods
• Audio feedback
• Visual feedback
• Show-off effect
• Emotional effect
This is much much much harder to achieve. None of these things can be accurately analyzed. It is a touchy feeling kind of thing. But you can evaluate the results of your effort. You know you have good UX when people describe their feelings about the product.