Most interesting, engaging class I have ever had was Philip Greenspun's short database class at MIT. All day for three days, a cycle of ~15 minute lecture, ~15 minute problem sets worked by each student on their own laptop, ~15 minutes of reviewing student solutions (and, if needed, presenting the "correct" solution).
I imagine that many classes could be presented in a similar format. I also imagine it would be a lot of work on the part of the educators to do this.
+1 also had a professor who did this for his courses and it was a win. The theory being people only have ~20 minute attention spans, so instruction should be switched up as such. Result was I learned more, actually collaborated with classmates, and motivated me to prepare for class.
It was scheduled for 10-5 three days in a row, with a break for lunch, and a short break in the morning and afternoon. One of the days included a ~1-hour guest lecture from Michael Stonebraker, which did not fit into the lecture/problem set/review format. The last day fizzled out from the format a bit early, concluding with some random discussions.
I imagine that many classes could be presented in a similar format. I also imagine it would be a lot of work on the part of the educators to do this.