Slashdot's moderation system is quite unique. It's fairly hard to get mod points and they expire quickly, so brigading is almost impossible. Posts have a very low mod cap (5) as well so it stays fairly flat. There is also a meta-moderation system although it's never been clear to me how effective it is.

Probably the biggest thing keeping it in check is that they still a fully editor driven website. No article shows up that hasn't been seen by someone at Slashdot HQ, so it's nearly impossible for trolls to flood the zone with hate speech, and even if they try it's easy to filter out by just changing your post threshold. Also, the community is so small these days that nobody would even bother.

The +5 to -1 range was a great idea as it made it harder to suppress a controversial opinion by burying it in downvotes. It still stands out as one of the best systems I've seen although I'm not sure it would work on something like Reddit. It would probably work well here though.

I was active on kuro5hin around the same time and that had a story queue where anyone could submit stories and other users could approve, disapprove and suggest changes; when a story hit a positive or negative threshold of approves - disapproves it was posted or deleted, and if didn't hit either within a week it was also removed. Again the thresholds were higher to get a story posted and to get it rejected, and only users with enough positive karma could see the queue at all. That worked pretty well.

In the early 2000s I was active on the "hidden" sids such as trolltalk where people would troll Slashdot and share it with others. At one point one poster ran a dictionary attack on the first 10k accounts using some very simple password guesses and captured several hundred or so - and then built a system that had them log into Slashdot regularly in such a way that they were most likely to receive moderation points, which were given to users who browsed regularly but not frequently. He then wrote an interface that wrapped Slashdot and allowed anyone using it to be able to moderate any comment there as if you had mod points, but actually by using moderation points from one of the pool of accounts.

If you ever saw posts with (Score 30: Troll) on them, that would be why...

The best thing that I love about the Slashdot moderation system is that you can't moderate and post in the same discussion.

It keeps people from simultaneously expressing their opinion and downvoting other opposing opinions.

It also only awarded mod points to people who browsed the site on a regular basis but not all the time - so logging in every day or two for an hour would give you them fairly often, but if you spent all day on there you never had mod points. I don't think I got them until I started to use the site less and less which was years after signing up in 2000.