I still miss Slashdot’s moderation (and meta-moderation) system.
For those who don’t know, Slashdot comments are scored in a range of [-1, +5] and upvotes and downvotes have a reason attached (e.g. +1 insightful, +1 funny, -1 troll). Users are given a very limited pool of votes to hand out, which are allotted according to a secret formula based on karma and maybe meta-moderation. Meta-moderation is a volunteer task where you’re given an anonymized list of comments and mod votes, and asked whether you agree with reach of them or not.