(i) In the calculus videos, when I viewed them, the graphs were drawn very shakily, extremely hard to understand, and not well labeled. Also, the low intensity of the videos makes it easy for a person to watch them when tired and distracted without missing out on too much. It also makes it easier to scale up and make a larger quantity of videos. This may not be completely a minus, because the lack of polish and the chumminess of the videos might itself be an endearing factor that makes people more comfortable with the videos. It is not really comparable to how an expert teacher would convey the material. Watching the Khan Academy is roughly akin to having a smart kid in your class (who is learning the subject along with you) explain to you what he/she has understood of the subject. What this suggests to me is that the Khan Academy is lacking in depth and clarity of presentation, as well as in addressing the subtleties and key issues that would be necessary to impress a person with some knowledge of the subject.

As a math graduate student and calculus teacher, I find Khan's math/calculus videos the least impressive of the lot, his physics/chemistry/biology videos mildly impressive, and his history videos the most impressive. I find that the impressiveness of a Khan Academy video for me is negatively related to how much I know of the subject.

Khan academy math answers