What did happen to HN, exactly? Maybe the bloom just hasn't worn off for me yet, but discussion here is about a million times more high-quality and productive than, say, Slashdot.
Comments similarly started lacking in quality, or maybe the really vocal minority are just louder than everyone else. You're right that slashdot comments are way worse (jokes aren't frowned-upon as they on HN, so a lot of discussions degrade to cheap jokes), but the articles are moderated by a handful of people and are typically more interesting.
It's simply a function of a user-run moderation system that reaches a critical point, after which is it logistically impossible for the "good few" to moderate out all the bad ones because their votes count the same. We saw it in Slashdot comments, Digg and Reddit, and now we are seeing it here.
It'd be interesting to see some statistics on who comments on what articles. (And who doesn't.)
As it stands I sort of feel like I'm crashing a party, and would serve you all best by leaving.
Aside from political posts, I think there is still a broad range of content on here that spans far more than myopic coding/entrepreneurial blogs etc.
The core problem with HN seems to be the tendency for people to lambast ideas before we've given them a chance to germinate. PG gets fiery mad at this behavior. Scoffing at ideas adds nothing, in fact it reduces the value of the conversation to the point that it has less-than-zero value.
To use a (poorly constructed) analogy: if I want to laugh at nerds and their nerdy ideas, I should go join the ranks of nerd-scoffers at any local high-school, where I'd be a better fit. If you want to be part of the conversion here, you should bring a positive or constructive voice and try to improve on ideas, rather than tear them down.
Great comments happen here too, but I feel (possibly incorrectly, haven't done a survey or anything) that they come on a smaller range of subjects. You can count on tptacek for very good crypto comments, grellas for law, there are some old-school Lisp hackers around, and on a lot of web-related stuff you have the people who wrote the system in question around to comment. But we don't seem to have as many non-computer technologists around: pilots, nuclear engineers, chemists, etc. I think Slashdot has a userbase that averages somewhat older, somewhat less Silicon Valley, and somewhat less startuppy, which has its pros and cons.
Or maybe it's just rose-colored glasses to some extent; certainly there was the "imagine a Beowulf cluster of these!" type stuff.