But the five vote options (insightful, interesting, funny, off-topic, troll) were _useful_. Having a feed based on the score of votes plus friend bonus, friend-of-a-friend bonus, foe penalty, friend-of-a-foe penalty gave me a super news feed I stuck with for almost a decade.
I could see a more complex voting rule set being helpful. But basically, it was really good until it wasn't, and that was a problem of the people behind the scenes there, and not the system itself.
HackerNews is comment driven, but does a decent job of facilitating discussions - but not particularly deeply. Reddit is similar. Forums are much more amenable to linear, deep, discussion between a few parties, but can also facilitate comments. Both have their place on the internet, and I don't think that forums are necessarily the answer to everything, but it feels like a lot of people left those communities to end up in Reddit and that's a shame.
If you reply to an earlier one, the UI will handle it and show a new branch where that conversation started. I'm not a huge fan of typical mailing list web UX and usually view flat, but it's so common that I guess a lot of people like it. My opinion is probably biased from years of using/running forums, so I'm much more used to that UI.
I think newer systems like Discourse will formally track replies to you (versus a new message in the overall thread), while legacy forums like PHPBB usually just quote-reply.