[jtbarrett]

Definitely agree, but I've had lecturers who take this too far. My intro. quantum physics professor was a brilliant and accomplished researcher at the bleeding edge of this field whose most basic concepts were deeply mysterious to us students. We appreciated the passion and keep knowledge that informed each of his tangents, but they were pretty impenetrable and very frequently distracted from the material at hand. I left the class thinking he was a brilliant man but fairly poor teacher. Then I had had him the next semester in thermodynamics and he turned out to be great! Certainly he had plenty of knowledge of the field, but he kept the class somewhere within the scope of the syllabus and relayed the foundations to us much more carefully. He focused on teaching, not the material itself.

The GEB lectures you linked are an interesting example in themselves. The early tangents that the teachers launch into on their own are certainly helpful, especially in such a free-form class. But student questions and tangents soon dominate that class too, to the point that I found it quite unbearable. When there is interesting material to be discussed they continually relapse into tired speculations of the "well maybe the universe is just a giant computer simulation" sort. The last lecture in particular is completely dominated, and in my opinion ruined, by questions from the most persistent student. A teacher needs to take charge and keep the class on track. Perhaps in a real class Justin would have.