I've been there many times and have had the same experience whenever I go...
It's a large open mall, so be prepared to do alot of walking. Also, it really is only worth going when they have sales (can't help you on that, sorry!) as all the designer stuff is pretty pricey without them. Though, of course, when there are sales you'll have a billion other people willing to forfeit their lives for a bargain and beating you to all the good merchandise.
Or you could try your luck and go whenever you want.
Either way the area is nice as it's far enough in the mountains to be nearby outdoor nature stuff (if you're interested in that) so your day doesn't have to be completely ruined if you don't buy anything.
Enjoy and good luck!