My kids (DD5 and DS3) loved the safari, Festival of the Lion King, The Boneyard, the train ride to Rafiki's Planet Watch, the talking trash can at Rafiki's, Triceratops Spin, It's Tough to be a Bug, all the animal trails, the characters, Donald's Breakfastsaurus and the bird show.
DD was absolutely terrified after our first safari which totally shocked me because I'm a zookeeper and we go to LOTS of zoos. It turned out she wasn't scared of the animals (phew!) but of the rickety bridge that is part of the lame-o poaching story. Once I explained that the bridge is just part of the Disney fun we thankfully got to do the safari again. Both kids could have spent hours at the Boneyard, especially in the dig area. We met tons of characters at Animal Kingdom and our whole family enjoyed the Donald's Breakfast character meal. We LOVE Animal Kingdom!!!