The problem started with the lateness of the submissions...easily trailing other sites by days at times. I quit posting submissions because they'd never show up, despite being fairly interesting topics on other sites.
Then the quality of the comments started going downhill, largely a product of the overall malaise that fell over the site brought about by the rather mentally torpid powers-that-be that ran the site.
To be fair to Slashdot, however, they have removed the "stuff that matters" tagline from visibility on their site (it's in the source).
That, and Hacker News seems to be about 3 days ahead of /. so it's kind of redundant to read it. Unless I want to learn about new keyboard shortcuts. I read Ars too, which is sometimes a bit behind HN but also covers different material.
[1] http://tech.slashdot.org/story/13/08/26/0010239/the-greatest...
Most of the +5 comment are traditional /. "meme" (OSS good, closed-source bad, MS bad, Google good, ...) and their counter of course. That has always been the case to some extend (that's /. DNA), but it has gotten to the point that it is extremely hard to find any type of information whatsoever just an endless battle of people throwing rumours (you would think that the majority of /. reader are board member of major tech corp), group-think opinion or unrelated info at each other to "win".
It reads now like a political blog for teenagers.
HN has great comment, to me that the closest to reproduce the /. experience of 10 years ago (although it could use a good flamewar between friends once in a while) But even the more chaotic reddit manage to show interesting comments on top.