Kids always love the zoo, but hot in the summer.
We live in the Houston area and have a zoo pass. It is about a 30-40 min drive and we still make the trek. I have three kids 4,5,9. When you get there find out the zoo keeper talk times on the map or posted if you want to talk to zoo keepers or see special shows. If you want to see the sea lion show get there early for a good spot right along the rail, or it is hard to see.
Don't miss the aquarium immediately to the right as you enter. Another great place is the natural encounters building. A cool tunnel for the kids, bats and real up close animals, inside. Plus my favorite, the naked mole rat. Since it can get really hot in Houston mixing the outdoor stuff with the indoor buildings gives you breaks through out the day. Also go first thing in the morning to avoid the heat and see more animals.
We don't use the map anymore because we know where everything is. I don't think it is a great map, but not horrible.
The back part is being renovated, but the zoo still has lots of stuff. Not anything crazy or exotic, but a decent variety. Lots of birds that we typically skip, except for the flamingos. Kids part has some fun interactive things, but also has some parts that need work.
Food is expensive in the zoo, but you can take in outside food and have a picnic on the grass or sit at the tables. We typically leave the stuff in the car and then walk back out to Herman park and have a picnic. Then decide if we want to go back into the zoo, they hand stamp, or go do something else.
Parent warnings:
1) the kids area has a water play area that kids get soaked in. If you don't want wet kids take a change of clothes or be prepared to tell them "no" It isn't open during the winter.
2) The entrance of the park is near the Herman park train. This is a separate cost.
3) In the zoo, there is a carousel that also costs a few dollars, like $2 or $3.
4) It gets really hot in Houston in the summer, the zoo is shaded and has misters, but have water on hand because the water fountains aren't always easy to find.
Parking is free.
I have been to better zoos and worse zoos, I find the value to be good if you plan on spending the day and have kids. I don't know that I would put it high on the list for just adults, we have nice museums. However, if you have some time it is good for the price.