This park is beginning to grow on me. I didn't really like it the first couple of times. It is very beautiful, and now I feel bad for putting it down to friends and family who have gone to the World over the last few years.
AK has never been an all-day park for me. Usually I am with my mom who is 56, and her opinion is about like mine. The Festival of the Lion King is a must-see. Kilimanjaro Safaris, too. It's Tough to Be a Bug is very good. I haven't done Kali River Rapids because I don't like to get wet, but it's probably fun if you don't mind getting wet. Tarzan Rocks is enjoyable - I'd go just to see the skaters. Dinosaur is not exactly fast, but it is dark and kind of rough. We really like it, though. IMO, skip The Dino Rama area. The rides aren't very fun for adults and it's one of the least attractive places in all of WDW. Flights of Wonder (a bird show) is worth doing once. There are some trails you can take that have lots of animals (gorillas, tigers, bats, etc.) that you probably won't see on the safari. I'm sure I've left out something major, but I can't think of anything else.
Be sure to visit the Animal Kingdom Lodge. It is an attraction in itself. Eating at Boma is worth every penny.
One word of caution: when it's hot down there, this park is the hottest and steamiest. I hope you are going at a not-so-hot time of year. Otherwise, get there as early as possible the day you go and drink lots of water.