Almost 95% of the people I know like to visit zoos, and the London Zoo is a very nice place. Like some people have said when visiting the London zoo, is that it is not in a pretty neighborhood, but overall inside the place is what matters and they liked it a lot. There are lots of animals in the London Zoo, and it's estimated that there are over 625 animals, so you won't get tried of watching the same animals again and again.
I really like seeing the gorillas because they are so big, but if you observe them they have lots of quality's from humans. There's always lots of people in the London Zoo, but it also depends in what season you go. In the zoo you can also find some weird bugs, which I don't like myself, but if you are interested you can always take a look. Overall the London Zoo is a nice and calm place you can visit when you have the time.