I think the only better zoo experience I have been to is the San Diego Zoo -- which says a lot about this place. The first impression I had when coming here was thinking it was going to be crowded because parking was difficult. The lot was full and people were down to making their own spots wherever it made sense.
Upon entering, however, we found out that this place is HUGE. Crowds were not a problem and the exhibits were all done very well. There is construction going on so it is obviously expanding even further in some places.
The only downside (using the San Diego Zoo as a comparison) is you do not get the sense that there infrastructure for managing people has come up to par with the great job they seem to do for the animals. I think this will work out over time but that is the only thing keeping that last star away from this rating.
As a bonus for the day we were there the Thunderbirds performed part of their show over head as they flew in and out of the actual Luke Air Force Base show center.