In its heyday, Slashdot was often (but not always) really timely with tech news, and was reasonably well-curated. The comments were generally numerous, and had a lot of genuine insight since the site tended to be frequented by actual IT/development professionals. Even the political discussion was fairly sincere. It also had an early user-driven moderation system, which while flawed, was enough to separate the wheat from the chaff. It anticipated Web 2.0 in a lot of ways.
I used to click on big posts, set the filter for Score: 3 or higher, and read through EVERYTHING. It'd take hours sometimes, and I'd learn a ton about all kinds of stuff. These were discussions, not just comments, and I think people took more pride in the quality of their contribution.
Like everything from back then, Slashdot got whittled down. It went through multiple acquisitions, and eventually became disconnected from all the original people behind it. Subsequent owners seemed to have no vision or connection with the community. There were some attempted changes that never seemed to go anywhere, but I think the most important thing about the acquisitions is just how bland the site became.
And of course, even if Slashdot had all those same people, everything else changed too... the industry, the people, the culture, the Internet, the whole world.
HN is the closest thing I know today to /. -- I'd say imagine an HN where editors curated the content, and with a lot more whimsy in its culture, and a lot more optimism. I don't expect to find any of that today on Slashdot, and when I do click through to the comments I find them to be very one-dimensional and tired.