I like zoos, and this is good and big one. Actually, I don't understand how someone can say it is small (maybe they just didn't see all of it?): if you want to see everything, it can be hard to do it in a single day.
First, the animals, of course. It is quite complete, with a lot of species from Asia, Europe, America (specially Brazil, of course) and a LOT of African animals - and I'm talking the big ones here: elephants, lions, rhinos, hippos, giraffes. The reptile house is small but has some remarkable animals (like a python) and there's a butterfly garden as well. The sad part (for now) is that the big hit of the zoo, the gorilla Idi Amin (for a long time the most isolated animal in the world with the nearest gorilla in Mexico) has died. Still, there are 2 female gorillas now and they have a world class habitat space.
Second, the plants. Trees and flowers everywhere. It is a zoo-botanic foundation after all, so if you're not really into the animals, you can still enjoy this part.
Now for the problems: it can be confusing (not enough signs for its size) and it lacks some infrastructure (sometimes you'll find yourself walking on grass or dirt to get where you want). Also, it can e packed on the free days - it is not expansive and your money goes to animal/tree related research, do yourself a favor and go in a regular day. I'd say that it is a good option to bring your own food too.
If you own or manage Fundacao Zoo-Botanica de Belo Horizonte, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.