My fiancé didn't like zoos before we visited the San Diego Zoo—in fact, she was reluctant to visit this zoo with me despite its famous reputation. She left with a completely different opinion.
The San Diego Zoo offers fun for all ages because I can't think of any animal or exhibit they do not feature. It was a lot of exercise walking up and down the hilly terrain, but sightseeing buses and a Skyride are also available and included in some admission packages. I don't think I have to go into great detail about the animals we saw, as they had virtually everything under the sun. The one thing that we did not get to see because of construction was the tiger exhibit, which disappointed me, but this did not ruin the experience at all.
The highlights: seeing a very young panda cub, which we learned was a rare sight in the United States; the polar bear exhibit; and the gorillas, because we saw the male rise from a sitting position to standing on his hind legs while he was less than 10 feet from the viewing glass... he must have been 9 feet tall!!