I grew up down the street from this zoo, and have seen it change quite a bit since I was a kid. There are fewer animals now than there were (which sounds like a bad thing, but I think it's turned out well, since the animals are housed in much larger enclosures now). The African Savanna's great, with the opportunity to view animals from an island in the center of a watering hole, and Grizzly Gulch is awesome. They've also done a lot of great conservation work with local species, releasing bald eagles back to the wild; a hidden gem in the corner of SF!
This zoo is a great resource for children and their parents in the SF bay area. Besides the traditional animal exhibits and scientific information, they are really trying to get a conservation message across to visitors. From graphics with pictures and stories of real people making a difference at the Africa and Lemur areas, to hands-on composting and backyard habitat activities for kids, they inspire young (and some older) people to make a difference in the world. The children's zoo (with summer Nature Trail program) is the real gem of this zoo. With so many hands-on exhibits and a wide variety of ways to learn, kids learn not only animal information but also a feeling of wonder and stewardship for nature. Yes, some of the exhibits in the main zoo are outdated. But the newer exhibits are excellent, and you can't expect them to change everything at once. Here's hoping they continue to improve.
With penguin-feeding shows and a great bug exhibition, the zoo does inspire kids to consider the world around them. Some of the animal pens are borderline depressing-- but the animals look healthy, if bored. I appreciated hearing the reasons that some of them couldn't survive in the wild (such as a falcon with a warped wing); it made the circumstance of imprisoned animals seem more beneficent.