I've been reading slashdot for quite awhile (notice "cough cough" my 5 digit Id, and I was an AC for awhile before I signed up.)
The changes in slashdot are to some extent part of changes in the internet itself. More people are interacting now, and younger people, certain tropes or memes or whatever have gotten established, and in some cases become old hat and shrunk away.
Things change, period. I'm nostalgic for the hey day of Usenet, the late 80s. But if I went back and looked at old usenet posts in google groups I'd probably be underwhelmed, partly because the topics from then are dated (flame wars in rec.audio over tubes vs solid state or digital vs analog), or otherwise thrashed over so often that everything got said thrice over. Part of it would be that I've changed too. If I went back and looked at an archive of early slashdot posts (is such a thing possible?) I'd probably get the same feeling of being underwhelmed that I do with usenet. (But slashdot hasn't degraded nearly as much as Usenet has. In fact, I'm not sure I'd say it's degraded much at all, just changed.)