Also, in contrast to their website, their Youtube channel only contains educational videos and no promotional material. They also have a German channel [1], which unfortunately is not up to date with the English one, though.
If you like this kind of dense educational videos I can recommend C.G.P. Grey's [2], Crashcourse's [3] and Henry Reich's [4] channels.
I'm fascinated by this new avenue of educational material as it can provide the best parts of both books and tv if done well: You can pause and play back any parts you have difficulties to understand or want to think through more thoroughly and you have the benefit of both visual and auditive information channels in parallel. For example of the latter, take a look at this video [5] - describing the same concept (expansion of the universe does not have a center) in book would have been much more awkward. Also, the pure speed of the videos makes them more entertaining than any TV show could, because TV has to aim for the lowest common recognition speed at every time. E.g. [6] would never be possible on a streaming media.