From the last four years: (I'm a professional critic, thus watch almost everything)

1. Gunda. A mother pig.

2. An insignificant man. Politics in India.

3. Mr Bachmann and his class. A teacher.

4. Icarus. The doping scandal.

All time:

https://letterboxd.com/rurban/films/ratings/genre/documentar...

Gunda, The real dirt on Farmer Joe, Models (Seidl), Warheads (Karmakar), The Land of the Enlightened, Close-Up (Kiarostami), The Wild Parrots of Telegraf Hill, ...