This is an in-depth treatment of what's important, and how to effectively conduct and benefit from, game playtesting. Translating the 6.5 hours of videos to words, it's the size of a small novel (more than 50,000 words). To my knowledge, there is nothing approaching this size on this subject in existence.
Playtesting is the heart (though not the brains) of game design. If you want to be a good game designer, not just a hack, you have to understand that heart just as you have to understand the brains, as covered in my other courses.
The major sections cover:
What is Playtesting?
Arranging the Playtesting
How to Conduct Playtesting
How to use the results of Playtesting
Other Considerations when Playtesting
There is nothing here about game programming, art, sound, etc. It is all about game design.