Dinosaurs! They pack in a lot of different species, including several of the gigantic ones like the T-Rex into the exhibits. They make good use of the space they have, and it was cool to see how big (Or small) the different dinosaurs were compared to your own size.
There are multiple levels, each one packed with all sorts of information on natural history, both world and Arizonan. In addition to dinosaurs, they have history on the Old West, geologic formations, and native Southwestern culture, just to name a few.
Overall, a cool place if you like dinosaurs, or if you want to spend a nice informational outing with the kids.