I taught a course on Galois theory at Canada/USA Mathcamp. The context was certainly different from a regular university or college: there were no exams or evaluations of any kind, and students choose their own courses and drop casually out of them if they wanted. I started with 28 students (many of whom did not belong there), and ended with only 14. I think that 10 out of those 14 had learned a significant amount of material rather than being over their heads, and 4 out of those 10 understood everything we had done perfectly. When you compare this with the outcome of teaching a course on Galois theory with traditional method, it is not bad at all.
It is true that the material is covered slower than we traditional lecture, but I believe that students learn more. The students who finished the course were certainly enthusiastic and I had the same experience that Kevin tells in his last paragraph.
Finally, I will add that a competitive atmosphere is not necessary for the Moore method to work. (Yes, Moore's original course required aggressive and competitive students, but there are many things we call Moore method now.) In my case, it was more of a community working together. I recall how, after proving the fundamental theorem of Galois theory, a student was attempting to compute $\cos \frac{2\pi}{17}$ explicitly (in an afternoon, preparing for the class for the next day), and he was surrounded by a group of other students, eager following the process and cheering him on.
In short, after my limited experience, I am a bitbig supported of the Moore Method and other variations. Particularly for students who want to go on to become mathematicians, it gives them a more realistic taste of what math is than a traditional course.