[TomGullen]

I loved Koyaanisqatsi, trailer here: https://www.youtube.com/watch?v=PirH8PADDgQ Not your typical documentary.

Anything by Werner Herzog is incredible as well, I find his approach extremely sympathetic and respectful to the subjects but without sacrificing detail (EG Grizzly Man)

Not strictly a documentary, but Threads by the BBC is a researched film depicting life in the UK if every city was hit by a nuke and it was incredibly disturbing and informative: https://en.wikipedia.org/wiki/Threads_(1984_film)

Carl Sagan's Cosmos has to be one of the most charming and moving documentaries I've ever watched - arguably a little out of date now but it reached a place the subsequent Cosmos series just couldn't reach.

MayDay! Air crash investigations are all amazing documentaries that manage to balance pretty intense technical information with real life suffering very skilfully and they are incredibly engaging.