What makes a good grad seminar?

Both in response to Mel's post on graduate education, and in the aftermath (afterglow?) of a terrific seminar yesterday afternoon, I've been thinking about what makes a graduate seminar good. Like Mel, I've viewed many of the ones I've attended as negative examples, but I want to concentrate for now on the positives: the moments when I, as a grad student, have felt engaged both with the professor and with the other students in a seminar.

Two examples leap to mind. My seminar yesterday was led by a professor who was not afraid of confrontation. He was never hostile, but he clearly had thought about the material extensively and was willing to call students out when they expressed views that he disagreed with, engaging them in dialogue about where in the text they found evidence for their position and pressing them to clarify terms they used with some degree of nebulousness. At one point, he even stated to a fellow student, "I think you're saying that because you haven't really engaged with Kant's argument." My impression is that this teaching style created a sort of safe space, in which we as students knew that if we said something fuzzy or expressed confusion about an idea, the professor would let us know whether or not we were on the right track. Now, this is a philosophy seminar, and perhaps philosophy is easier to negotiate in this way than literature. Thoughts?

My second example, though, did take place in a literature class, but again, one in which the professor was not afraid to guide students through his own methodology, research tendencies, and interpretations via quite pointed questioning. This isn't to say that he dismissed alternate interpretations or methodologies, but the point of the class was clearly expressed: it was oriented toward cultural history, and even if one's ultimate goal was not to read literature via cultural history, the professor's dedication to this methodology certainly (to me, at least) made it an appealing and valid point of view to consider for the duration of the seminar, if not longer.

In other seminars I've taken, professors seem to think that guiding a discussion with a strong hand and making their own opinions clear might be equated with treating graduate students like undergraduates. Taken to an extreme, that might be the result. But I can testify that I'd much prefer a course with an expressed goal and point of view to one where I'm assailed with the opinions of other graduate students without any feedback on which comments are weaker or stronger.