I really enjoyed visiting this zoo. The animals are grouped by "bio climatic zones" which is a fancy way of saying regionally appropriate. The layout is very intuitive, however, and one region blends very well into the next, making a walk through feel seamless and peaceful. The enclosures are generous and beautifully designed, while the spaces outside of the exhibits often feel like a scenic overlook where you just happened to spy a giraffe ambling by. Give yourself time to absorb this enormous park and try to go at an off time when you won't be overwhelmed by crowds.
Mid morning is probably the best time. I was there in the late afternoon and most of the he animals had punched out for the evening by that time.