The comment moderations are a little too generic. I say give a much wider range than -1 to 5. At very least make it -2 to 10. I'd personally perfer it go from -10 to 100. For this to be feasable mod-points would have to be given out much more often, but I don't see that as a problem.
Next I would take advantage of Slashdot's already built in friend system. You should be able to see both a friends' score and an overall score for comments. So you could setup your account to only take into account your friends moderations, or do a combination of the two. People constantly disagree on proper moderations, so this would help I think.
Lastly, I'd add a whole lot more comment labels. You should have an orthoginal design of sorts. If a post can be rated "funny" then it should also be possible to rate it "unfunny". Insightful? How about Uninformed? Stuff like that... How about a "zealot" mod option? Or with things like the GNAA around maybe it's time for a "Spam" label? I'm sure there's lot of new possibilities...
Any other ideas? Care to make a counterpoint (not flame)? Leave a comment below.