These are suggestions I would make to change the Dark Knight class, these are not something I would ask to change all at once, but these are to make the class more fun altogether and more practical compared to other tanks. Right now I believe they are unpowered compared to both Paladin and Warrior for plainly obvious reasons.
I stayed with the life-tap theme, however I also added some penalties to the abilities. Giving them a more unique flavor altogether.
Darkside:
Remove the Aura effect altogether and replace it to something like this:
http://www.youtube.com/watch?v=WGw_fqmzfgA&t=0m25s
Give it a health cost instead of MP cost.
Reprisal:
Lower cooldown to 15 seconds.
Lower potency to 160.
Blood Price:
Sacrifice 15% of your life over time for its duration.
Restore 50% of your mana over time for its duration.
Instant Cast, 40 second cool-down.
Blood Weapon:
Sacrifice 15% of your life over time for its duration.
Increases attack speed by 15% and converts physical damage dealt into MP.
Can now be used with Grit.
Instant Cast, 40 second cool-down.
Dark Arts:
Additionally removes the damage penalty of Grit for the ability your using "Dark Arts" with.
Shadow Wall:
Reduces damage taken by 30% and restore own HP with a potency of 50 every time you suffer physical damage for 15s.
Instant Cast, 120 second cool-down.
Salted Earth:
Creates a patch of salted earth at your feet, dealing unaspected damage with a potency of 100 to any enemies who enterand restore own HP with a potency of 75 for each foe hit.
Dark Mind:
Gain the ability to block.
Modifies Block Rate by 4*level: 240 at level 60.
Modifies Block Strength by 10*level: 600 at level 60.
Dark Arts +:Additionally gain a dark shield which prevents damage.
Duration: 15 seconds.
Instant Cast, 60 second cool-down.
Living Dead
Duration: Forever.
Yes, it is now a death prevent. =)
Ofc, you still die if your not healed fully.
Souleater
Delivers an attack with a potency of 100.
Combo Action: Syphon Strike, Combo Potency: 260
Dark Arts Potency: 240
Dark Arts Combo Potency: 400
Grit Effect: Absorbs 100%(200%) of damage dealt as HP.
Dark Arts fades upon execution.
Power Slash
Delivers an attack with a potency of 100.
Additional Effect: Increased enmity
Combo Action: Spinning Slash
Combo Potency: 300
Dark Arts Combo Potency: 400
Dark Arts Additional Effect: Forces target to target you for 3 seconds.
Carve and Spit
Reduced cool-down to 16 seconds from 60.
Delivers a threefold attack with a potency of 75. Also restores MP if used while not under the effect of Dark Arts.
Dark Arts Potency: 250
Dark Arts fades upon execution.
Sole Survivor:
Guards the target while it remains within 20y. While active, the target takes 5% less damage and generates less enmity and you gain 10% base parry when you are near the guarded target. Requires Grit. Cannot be used on players using Grit Stance, Shield Oath, or Defiance.
Cool-down: 120 seconds.
Duration: Forever.
Cast Time: Instant.
If the target dies you gain a buff called "Vengeance" which increases damage done substantially whilst also increasing enmity gain.
Duration: 10 seconds.