What a great children's museum! My kids (3 and 4) have been there twice and have loved it each time. Both times we have taken about 4 hours to go through pretty much the whole thing, spending at least a little time at each exhibit. If we lived in Phoenix, it would be worth the price of a membership for sure!
As it is, it can be pricy. But keep your eye out for deals and know that kids of a variety of ages will love it!