I exclusively played a DoK up to Rank 15. Renown Rank 10 during Preview Weekend and this is the class I will be playing at release. The DoK is a very strong melee/support class, and in that order.
Damaging enemy players is a very important thing; a DoK standing in the backline is not the proper way to play this class and will not benefit your team.
The DoK play style is centered around a mechanic that we all know as life leech. This mechanic is best known from the game Diablo2. In WAR the DoK can store up to 250 ‘soul essence’ at a time and use it to restore health through the use of 2 main abilities. A minor heal with a HoT (Restore Essence), or a strong HoT (Soul Infusion). In my experience it is best to pre-HoT allies you know are going to be taking damage prior to engagement with the enemy, a full soul essence bar is not going to help as the majority of your melee attacks leech soul essence and so there should always exist a buffer for the overflow.
The third heal and the one you will be using most of the time is Rend Soul. I cannot tell you how excited I am about this ability. Its primary effect is to deal 4 hits over 4 seconds, but each successful hit heals your defensive target for 250%!! In the RR6 Tier 2 RvR gear I was healing for an average of 150-200 per hit! Now finally an ability that increases my healing power as the amount of damage I deal increases.
When you run out of soul essence, you can restore it by attacking a nearby enemy with abilities that restore soul essence, or by converting action points to soul essence. Out of combat soul essence regeneration is fairly quick.
The DoK also gets a snare mechanic, but it is not as simple as spamming hamstring. Applying the snare requires your enemy to be already debuffed with a cripple ability, which is a DoT called Lacerate., which is another mechanic that requires a player to be at the top of their game and prioritize their use of abilities.
At later levels the DoK play style follows these same core ideas. The amount of healing you can provide to your allies is proportional to the amount of damage you deal, and limited to the amount of soul essence you have.
DoK Secondary Abilities
A DoK is also classified as a support archetype. A Covenant is the same as an aura, and the DoK gets several very beneficial Covenants. The first of which is a group armor boost. AC makes a big difference in this game as it lowers incoming damage from all physical sources.
My Morale ability gave me a powerful single target heal at level 1 morale and a decent aoe group heal at level 2.
A DoK can also Rez and gets a group heal morale ability at rank 40 (awesome)
My PoV
This class is so ME. I have also been a melee dps type of guy (CS 1.6 roots) with a knack for staying alive/getting out of hairy situations. There is an incredible amount of adrenaline felt from the initial rush alongside your melee dps/tank allies, while also realizing you have the power to sway the course of the battle with your healing and morale abilities.
The downside is, you won’t likely get heals from a true healer as they will be occupied with the classes that cannot heal themselves. You have only yourself to rely on, but with great group synergy. A properly specced and geared DoK, which does not in fact mean you need to spec for healing or stack healing bonuses on your gear like a madman, but as such you have the toughness and survivability to take place in the initial charge and stand alongside the tanks and physical dps. A tank is very easy to keep up, and this is the strongest pairing for a DoK.
Another role the DoK can play is that of a rover (if you ever played softball). A rover stands between the frontlines and the ranged catching anything that tries to break through the ranks. This give you access to both the ranged and melee, while keeping you out of the line of fire (believe me anything that heals is going to get focused on) allowing you the time to build up soul essence and dish out heals.
All in all, a powerful and needed class.
Glimpse these vids for a demonstration of the action a DoK can expect.