The thing that made it good was the camaraderie, the general helpfulness, and the quality of posters. You used to be able to find some really intelligent content in the Slashdot comments, since some the smartest people related to that particular topic were probably Slashdot users themselves.
I still visit it every day just to skim the articles, but only about 20% of them are interesting/something I didn't see posted somewhere else.
Smarter moderation might work here in the short term, but ultimately the only thing that works is quietly sneaking off to a newer forum.