Fashion Show mall is the best mall I have ever shopped at. They have a huge selection of stores, that range from luxury (Neimans and Saks) to cheap (Forever 21). In addition to the typical major chain stores such as Gap and Express, they also have more specialty stores such as ilori, True Religon and Lululemon.
If you are visiting Las Vegas, it is worthy our while to make a stop here. They also have a couple decent places to eat (Ra sushi and Maggianos).
The layout of the mall can be a bit difficult at times, as there are three different levels, that don't always connect. If you are driving here, parking can be a bit of a pain during peak times. Overall great mall, but don't expect your stop here to be quick.