While I've watched my fair share of David Attenborough nature documentaries, I tend to gravitate towards political documentaries, or documentaries about significant events that I remember. Examples of recent docs I've watched are: Once Upon A Time in Northern Ireland, State of Chaos, The Rise and Fall of Boris Johnson, and The Space Shuttle that Fell to Earth. When I had Netflix, I did watch a fair few of their true crime documentaries, e.g. The Making of a Murderer, Don't F*** With Cats: Hunting an Internet Murderer, The Keepers, etc.

As for what makes a good documentary... I want to learn something new about the subject. Most of the political/event-related docs that I watch are about subjects I already feel I know a fair bit about, so I want new information, new perspectives or insight into the topic, etc. I also like it if my preconceptions are challenged -- it forces me to think and rethink, and that's usually a good thing.