Power Word Kill in current content is as the name implies, it will instantly kill a Mob or Orange named sub boss as long as the caster bypasses the targets Spell resistance.
This spell was a 'decent' spell for epics as it allowed the caster to 'take care' of that one big Orange named melee but at the expense of a very, very long cooldown.
With the Hard to Kill update coming on epics with U14 outside of normal epics this spell is taking a real hit, previously it was good for that almost guaranteed 'One shot kill' now it will be one of the lamest spells in the game.
I really think Turbine should look at doing two things for it:
A: Shortening its cooldown a little (2/3s of what it is now, or whatever)
B: Allowing it to bypass the Hard to Kill mechanic.
Just some thoughts on this one spell, I'm not totally for this new Hard to Kill mechanic as I just finished levelling my PM again for this update and it really does seem to me that Sorcs are going to be the big winners from this update.
Previously it was almost like PMs, Necro Specced Wizards better at killing mobs in epic than Socerors (just) and far behind on Boss DPS, now it's just Sorcs = Best at everything in Hard Epic and above. But of course this is all for one of those other threads.