Bring your camera, and wear good walking shoes. Depending upon time of day and what the animals are doing, this is an opportunity to get very close to them - much closer than most zoos allow. The entrance fee is going for a very good cause. You can get an all-day pass and come back later if you have arrived earlier than feeding time and want to see it.
I especially enjoyed watching the grizzly bear playing with his huge ball, and watching the macaque eat his meal. I admire cats of all descriptions, and there are many of them there to see.
If we are back in that area, we would definitely visit again.