Honestly id say

Dark Arts needs a cost decrease
Dark Wall needs something on it--its got the worst parts of vengeance or sentinel. Maybe it should Trigger Dark Arts for free?
Shadow Skin: Is Fine
Dark Dance: Inferior to Keen Flurry. Actually its pretty funny. For 30 more seconds they get 50% more parry---or compare it to another rank CD. Raw Inuition for Warriors is also 90 seconds and it parries EVERY attack for 20 seconds (and gives them a rage/abandon stack).