Apart from a few niche-specific closed forums, I've had consistently high quality discussions on HN. Somehow the HN culture stops the proliferation of low-effort comments and trolling so prominent everywhere else.
Ruthless but fair moderation, clear goals around what the community is for and hard working moderators.
Online communities are like gardens, they look best with constant maintenance and the odd pruning.
Eh, I much prefer using an app on mobile. All the buttons (up-/downvote, collapse) are too small, and a lot of space to the right is often left on the table, which makes longer comments very hard to read.
The discussion culture is what makes me read HN nearly every day. The comments are often more interesting than the articles themselves.
This. I often find myself going to the comments first, and then open the article.