They deliberately make them ambiguous. Matters like black holes, parallel universes are still unresolved and highly debated. These documentaries just explain different views regarding these matters as concrete proof is yet to be found.
I am eagerly waiting for James Cameron's documentary about his dive in Mariana trench. He is first human to go down that deep.
It came out today, search for 'National Geographic James Camron Voyage To The Bottom Of The Earth 720p HDTV x264-EDUCATiON'
There is this torrent pack floating around with the title '50 Documentaries to See Before You Die'. Has got some critically acclaimed and popular titles within it.