Well after spending a few hours on THM23/24 and doing a few behests and leves I have to say I love the changes. Scourge is easily doing double the damage it used to, maybe slightly less than double but still very noticeable. I barely notice an issue with the double MP cost on it. Scourge II however doesn't deal enough extra damage to justify the MP in my opinion.

When it comes to the heals, I am noticing I use Cure more than Sacrifice but I like that it gave me a fresh way to play. Now I use Sacrifice when the tank get's to yellow or red HP from a TP move or bad crit hit and save Cure for myself if I need it or for other players who don't have hate but got hit from AoE or something. I use Siphon MP whenever it is up and when I hit very low MP I use my 10min 1/2MP restore (name escapes me). I have yet to have an MP issue at all. HNM's would probably be a little tiresome on it but if the DD are smart to avoid AoE and you have a CON or another THM there to help when you're getting low, I foresee no issues.

Edit: Also Stygian Spikes has a great use now too.