As a parent I have not had experience with it, however, I have worked at schools where it is taught and really like it. If my kids had been school age when I taught there I would have been thrilled to have them in the program.
Done correctly, the program does make the kids think critically and see the world around them in a different way. It is great at generating thinkers and more independent learners. The culminating project in grade 5 is a big bonus of the program, in my opinion, because it allows the kids to delve really deep into a topic that is interesting and intriguing to the kids as well as giving them a chance to do some real research and presenting.