The navigation would have been simpler if they had united it under one channel with divided playlists. From what I can tell - the main user posted the initial video, and every video it links to is on another channel, a channel which has all of it's videos set up as unviewable, unless you're linked through by the initial video. That made it sort of annoying - if it had all been one channel with public settings on the videos, that would have been easier. I can't imagine the reason for setting it up for they did.
It's neat though!