I'm a little hesitant to enter into this discussion, as I am not a Catholic, and not even especially Christian, in a religious sense. But I was raised Catholic, and went to Catholic schools most of my childhood, so I feel I do have some idea of their catechism.
What did they get right? I would have to say that their schools are pretty good. They keep order in their classes, they pay attention to all the students, and to their family situations. They care about the well-being of their students both in and out of the classrooms. They hire knowledgeable teachers and their use of student uniforms serves everyone wisely. They do teach the Catholic religion, but they also teach well-rounded and informed non-religious curriculum. I think there is no doubt that their K-12 schools are excellent, and are superior to even many of the better public schools.
What did they get wrong? Where do I begin? For me, their biggest mistake was to set up a religious organization that is hierarchical and militaristic in the sense that no one in the hierarchy is allowed to question anyone above them in the hierarchy. Any system involving and operated by human beings will inevitably be subject to a good deal of error, and the establishment of such a rigid hierarchy only serves to entrench and even justify those errors rather than seeking to discover and correct them. And the second (perhaps this should be first) thing the Catholics got wrong was to place the pope, a flawed human being, in the position of being Christ's "stand in". No human being has the degree of perfection that would be required to actually function as a stand-in for Christ, and presuming to allow someone to take that position is just begging for abuse and failure. And not only that, the Catholic church further falls into this flawed hole by claiming that the church itself is the representation of Christ on Earth! Thus they place themselves as some sort of gate-keepers between individuals and God. This is not only wildly wrong, wrong-headed, and dangerous, it actually becomes a horrible stumbling block for a lot of people.
I am no longer a Catholic, and will never return to that religious perspective as long as they insist on holding to these two extremely wrong and damaging positions. And I see no reason to imagine that they will change. So we are permanently parted. Though I thank them for a good basic education, and for their honest help during a rough time in later years.