Saw my first ever gorilla, toucan, and polar bear (partial list here). It's also one of the most accessible outdoor spaces I've ever seen, with even an escalator segment that helps you navigate some of the steeper parts of the zoo.
We must have seen about 40-50% of the zoo, given the size of the campus. That's pretty much the most you can do in 4-6 hours, especially with children in tow. Which means you have to choose. With a dazzling array of choices, this act is very difficult. You have this problem at large buffets and bookstores (ok, *I* have this anxiety at bookstores).
People have been studying the problems of abundance - when we can't have it all, it makes us uneasy, for making a choice implies saying no to something else, and thus a potential loss - what if you made the wrong choice?
Sheena Iyengar's book Buy The Art Of Choosing sums this up nicely.