The major issues are:
No reordering of threads so you get the "first" posts stay on top for the lifetime, even if they're low quality. This tends to drive the discussion more than it needs to.
Only posting or Moderating. I can see the thought behind it, but it doesn't really make sense in practice unless the community is the exact right size. Either the community is large enough that there are more moderators to balance things out or the community is small and it reduces the moderation/posting because people can't do both.
This is necessary. If you allow people to moderate and post, people will routinely downvote comments that disagree with their own comments. This happens all the time on Reddit. Slashdot forces users to choose to between arguing their points (and generally getting wrapped up in their own viewpoints) and being the quality filter.
Similarly, random moderation is just a hinderance. I guess it goes with the rarely used meta-moderation, but that depends a lot on user interaction to work.
Random moderation is also necessary. Moderation should be an occasional privilege not another channel to participate in the thread as it is on Reddit. If volume is slow, as happens on Soylent, frequency of having mod points can be increased or we can accept that if traffic low, very little moderation is needed.
Reddit is hopelessly overmoderated. Redundant posts that express popular opinions are scored way up. Mildly descenting comments with real information and mod'd down to oblivion.
Too many moderation categories. It could probably be reduced to just 3 which would basically be: Good, Bad, Funny
Also necessary. The Slashdot system forces people to think about why they are moderating and expressly omits "disagree". Almost all moderation on Reddit is "agree" and "disagree".