Very small zoo and when we went, many exhibits were being renovated. My son's favorite part was the sea lion feeding. You can watch from the park walkway, so schedule your time right and you can see the best part for free. The children's zoo was pretty cool for the kids, and you get admission to both zoos with your ticket.
Way too big to explore it all in one day. The dinosaurs were really cool, but the exhibits about ancient peoples didn't hold the kids' attention much. I also wasn't enthralled by the space exhibits. The walkway from the planetarium was pretty cool, but we didn't go in the planetarium (walked up and back). It was really easy to get to via subway and right across from Central Park.
My husband was pretty excited to see this is where we were going after telling him we're going to another museum. It was pretty cool to go through the actual ship (not super easy with a toddler). Then there was the Exploreum where the kids can climb and explore. Overall, pretty cool museum!