The only thing that makes sense to me is two sets of dropdowns, instead of the up and down arrow. The dropdowns would have various positive categories "agree", "insightful", "humorous", etc. and various negative categories, "disagree", "inane", "troll", etc.

Instead of clicking up or down, you click the positive or negative attribute you use to categorize the comment.

What with clicking the drop-down, it's a two click system instead of a one-click system, but heck, to me it makes a lot more sense.