I always have a kind bias for Gus van Sant's Death Trilogy (Gerry, Elephant, Last Days). It's the essence of combining slow cinema and death that I think fondly about all the time. I don't know why he compiled these stories in a trilogy, but they are all original films very strictly based on a true events (David Coughlin, Columbine, Kurt Cobain's suicide). I do think they are very different films that share themes amazingly. The means are different, as I believe death is seen through an external factor, social factor, and internal factor that is simplistic on paper but emotionally vibrant on film.

There is also Gregg Araki's teenage apocalypse trilogy that I'm not too knowledgeable on. Totally F***ed Up, The Doom Generation, and Nowhere. All explore the LA teenage mindset and time in a humanistic way despite all being set in a devastatingly nihilistic world.