I find the Noise to Signal ratio on HN to be incredibly high.
For example, multiple posts per day[0] reminding us that facebook is 'bad' and 'spying on us' (no shit). When whatevercoin was a thing, there were many posts per day about how bit whatevercoins were the {best,worst,crashing,soaring,smart,dumb,future}.
HN started off with some direction, but now it seems to be turning into the fake internet point machine that many reddit sites are: where folks are rewarded for (re)posting whatever the 'hot topic' is of the month, and bolstered by millions of tangential or anectodal comments from people who never made it past the headline.
You can't post images inline. You can't embed links into text. Replies don't get forwarded to your inbox.
Simple things like that focus the site on the discussion and not on meme-building.
And it isn't really HN that is being additive. It is the community, being sensible and professional. It also avoid ( mostly ) all religion and politics debate, or basically things that is hard to argue about Right or wrong. Unless it is something that absolutely needs to be addressed, and the threshold for them seems to be very well managed on HN so far.
You also get huge ( And Surprising ) diversity of professionals on HN. Over the near decade of reading on HN, I have seen Doctors, Medical Research, Oil Refinery, NASA, Nuclear Research Scientist, Tunnel Building Engineers, Professional Musicians, Food Scientist, Chef, Collage Professors, Investment Bankers, Hedge Fund Managers... and a lot more.
I have often wondered, why are they even on HN? They don't speak often on technology related topics, but once you touch on their special subject they offer huge depth of valuable information that goes beyond any normal Internet comment. You will then spend next few hours or even days reading on lots of material before you could even comprehend most of that writing.
Reddit, while being fun, doesn't really have this sense of professionalism.