I grew up around the Omaha area and personally I think it is a GREAT zoo! There are TONS of things to see throughout the zoo and it doesn't feel like you are walking in circles without seeing anything. IF your children like fish, they have a great aquarium. I've heard good things about the coco key resort but have never been there myself.
If you do go to the zoo, make sure to take a train ride, it goes along the outside of the zoo and provides a background of some of the animals and the zoo itself.