In my humble yet accurate opinion, the San Diego Wild Animal Park is even better than the San Diego Zoo. It covers over 1, 800 acres and is home to about 3, 000 animals. The great thing about the Park is that the enclosures are huge, and many different species coexist within the same exhibits. The Park breeds many endangered species and has a huge "frozen zoo" where they store the genetic material of thousands of animals. There are many trails and gardens to walk through, and plenty of fatty foods to gorge yourself with.
I went with a friend last year and we decided to take a Photo Caravan Safari. The main admission price isn't too bad, but if you want to see the really cool stuff you need to cough up a hundred or more. The safari includes a "behind the scenes" truck ride through the large African and Asian animal exhibit where you get to feed giraffes and Indian rhinos, which is well worth the money. Here is a simplified summary of the good and bad aspects of the Wild Animal Park:
Negative: Walking takes up a huge amount of time. It can get super hot in Escondido, so bring water (the zoo water is super expensive) and sunscreen or you may just want to keel over and die.
Positive: This is a great place to see endangered wildlife in large exhibits. The place is beautiful and the Park has been successful in breeding many endangered animals.