For a free zoo, it's PHENOMENAL. When I first came, I really thought that it would be tiny, with uninteresting animals kept in horrid conditions. Instead, I was definitely surprised to see a fairly large zoo with tons of unique animals. It's the first time I ever saw a polar bear in real life! It was an awesome experience and I definitely encourage people to donate to keep this zoo active. If you're touring Madison, I would definitely spend a few hours here.
The parking is somewhat crowded and difficult, but street parking is available in the surrounding areas, so it's not too difficult to park. Overall, a fun experience with friends or even just by yourself to see some cool animals!