Once I worked in a team that used scrum almost correctly, and it was a great experience.

Then there was a change in management, and the new manager decided to "introduce scrum" to the whole company. We were told to stop doing what we did previously, and instead to do what the new manager called scrum. Unsurprisingly, it was the same parody of scrum that most companies use. The productivity plummeted, and the developers in our team gradually left the company.

I suspect that scrum works well when it is introduced by the developers, and works horribly when it is introduced by the managers.