Despite some limitations slashdot voting system is OK in most of the cases.
I'm fine with the mod-up/mod-down system for the most part. I do think that one account shouldn't have so much power to affect another account, especially through the karma system which is easily exploited by someone with no life. That one account can karma-bomb another into useless oblivion is a design flaw that couldn't possibly be what the coders had in mind, and that's the flaw that should get fixed.
It's not usually -1 Troll or Flamebait either, it's usually Off-Topic or Redundant that gets used. Things someone could individually look at and think "Well, that's a subjective opinion. I wouldn't have gone that far myself, but maybe you could make the case for it." Something that might look innocent in isolation, but when you gather all the posts and look at them as a group, it's pretty clear what's going on.
Like I said, I posted almost 20 years on the account without a problem, and now that account is trashed. Slashdot operates on a completely "hands-off" approach to administration, with no way to settle harassment, and that only works as long as you have the perfect system. As we've seen elsewhere, if you have no approach to handling harassment, harassers win. I've had a lot of my preconceptions about communication on the Internet challenged over the last year. I used to hold Slashdot up as a gold standard of discussion, but this site has definitely taken it's lumps of late.