If you're into human struggles and darker themes, here are a few I'd definitely recommend:
Dear Zachary: one of the most emotionally devastating documentaries I've ever seen. Go in blind if you can
The Act of Killing: surreal and deeply disturbing. It explores the Indonesian mass killings in a way that's unlike anything else
Grizzly Man: fascinating and tragic, about obsession, nature, and human psychology
Capturing the Friedmans: a really uncomfortable watch because it constantly makes you question what you think is true
The Thin Blue Line: a classic true-crime documentary that actually helped overturn a wrongful conviction
Tickled: starts off as something completely bizarre and ends up going to some very dark places
If you want something a bit different, Honeyland is beautiful and heartbreaking at the same time!!!!