This is the largest desert dome in the world (everything in Omaha is BIG) and it is simply spectacular in terms of size and scope. Some of the animal exhibits could definitely be larger, but overall it is quite the experience to stroll through the huge dome.
The Desert Dome combined with the Kingdoms of the Night below all of this in the same building makes for one of the most immersive zoo experiences I have had.
Toss in the Lied Jungle and everything else at the zoo and many people consider Omaha to be one of the top 5 zoos in North America. Everything there is so big...but others have pointed out that there are some serious detriments as well. Cat complex, bear grottoes, etc.