So well spent that it didn't even feel like 20 minutes. This is what videos should be like-- not essays delivered more slowly and painfully, but real useful things presented visually in a way that takes full advantage of the medium.
Sorry for the lack of clarity. I meant that the form of presentation should be useful for aiding understanding, not coincidental. I didn't mean to implythat the content itself should be useful (in the sense that it has practical applications). It's OK for a video to just be a little mental puzzle.
