As a family outing on a snowy Friday morning, this was fun. We paid $2 to check our coats, took a swing through the discovery center where our small son got to pet reindeer antlers, peer at a dragonfly wing under a microscope, and so on. The rainforest is amazing, the laurentian forest is pretty quiet, and the penquins are adorable. The good thing with a 4yo is we could turn him loose in each hall with the caveat "don't go through any doors" and let him run back and forth and back and forth while we looked more systematically.
It's pretty expensive, though, for the relatively small number of things to see - you can go around again, though, and we might have except we went to get lunch. I probably wouldn't go again, but we had a fine two hours peering at fish and frogs and eventually locating a lynx ear-point in a chilly landscape. I wished we had more time for the fossil room, but the need for lunch overwhelmed us all (protip: if you visit the cafeteria, stick with the soup and sandwiches.)