We live 5 minutes from the Seattle zoo, and out 3-year is obsessed with animals, so we go there several times a month. We decided to check out the Point Defiance Zoo. While it's much smaller than the Seattle zoo, we really enjoyed it. One nice thing is that it's an aquarium too, and our son loved the sea otters, Beluga whales and the mammoth walrus. He especially enjoyed watching the sea otters smash their food on the rocks (the Seattle aquarium has the sea otters in concrete tanks with nothing to smash food on). In the zoo part, they have many animals that the Seattle zoo does (and, of course, vice-versa), like polar bears. It doesn't replace the Seattle zoo, but we'll be back.
Pros: Interesting animals, Zoo and aquarium