Phantom Dart is a low damage (although still between 50-90 average, so quite potent compared to regular melee hits it counterparts). It has decent range and quite low stamina consumption so is very spammable. Builds TP up quite quick, in Alpha it was giving about 650 a hit but now seems to be around 200 to 250.
Dia and Scourge are great spells. They do quite high (200 to 250 against roughly similar level targets) and leave a debuff that weakens them to that damage type (so Astra for Dia, and Umbral for Scourge), although the weakness does not seem to increase much, maybe 5-10%. Much more of a group mechanic I recon.
Slow is extremely potent. It doesnt last as long as its recast but while its active on a mob its almost a Stop spell. Slowing a mob can make tough monsters very easy. Great spell! I can see in large party situations a Slow rotation between THMs, if it continues working the way it does now, to be a very used and powerful tactic.
Punishing Barbs at level 10 is, as others have said, fantastic if not OP. While it is up, all damage you recieve is dealt back to the enemy. So if they hit you for 10, they suffer 10 too. If they hit you for 500, they'll take 500 too ;P
THMs can cure using Sacrifice quite well. It differs to Conjurer heals in that it is an AoE targetable (Cure is conal I believe) and leaves a weak but noticable Regen effect on its targets. It costs 54HP as well as 10MP to cast and without any stat boosts heals for around 175 a cast, plus maybe another 50-75 over the regen period. The fact that it costs you health though means in a group situation you do have to heal yourself, but because its AoE I just pop in close and reap a few of my own casts to keep up.
THM is very MP sensitive and as others have said you tend to Phantom Dart/Damnation spam with the odd Slow and Sacrifice thrown in to keep your MP levels from doing a Titanic. Once you get to level 16 though MP becomes almost a moot point with Stygian Spikes. When these are on (they last longer than the cooldown so can be kept up ad infinitum currently) they return 23MP to you each time you are hit. Its a targettable spell so you can give it to other players too, although they recieve the MP if hit not you (which would have been cool!).
THMs are a weird class. Theyre very weak to begin with, probably the weakest of all DoW/DoM jobs. At level 10 when you learn Damnation your killing power goes up somewhat, but you're still not as good as other jobs. At the moment Id deffinately say THM is more of a support job than a DD job, although they can contribute decent damage if they are needed to. The fact that you can debuff, buff, heal and DD a little puts THM as some sort of RDM & BRD ******* child. Great fun to play as in a group setting once you get past those gruelling 15 levels of underpoweredness!
Feel free to ask any specific THM questions, I've played it pretty extensively since the first Alpha test :)
To endanger the soul endangers all,
when the soul is endangered it must become a Warrior.