I don't know what/when this happened to Slashdot, I remember that most of my life I have been avoiding the comments sections of almost every website, and then I met HN :) and life changed. This is perhaps the best self-curated forum and I believe that the main reason is that we all "got better things to do with our time", and we are coming here to exchange opinions and views with similarly productive people. Maybe this is it, most of us are productive and respectful of our AND other people's time and attention.
you have meta moderation divided among a vast population of users, who have to give up commenting rights for the article. you can filter for a variety of personal tastes (funny, insightful... even troll), a friend/foe modifier and so much more.
but yeah, the sanitized community and centralized moderation on HN or reddit makes for an /infinitely/ superior first visit experience, but after you log in and learn the minimum of the system (which fits nicely with the /. proposal anyway) it is in a completely different class.
on /. i actually learn some deep arcane stuff about a topic (and have a few laughs) as opposed to the serious HN hive mind, which i personally use in lieu of the (missing) article summary.