Yep. If you can cast it, then slam the door shut and wait a bit, PW: Pain is great at softening bad guys up.
Thing is, say you tag empower on it. Now it does 4d4 x .5 = 10.5 rounds average, 3.5 x .5 = 5.75 damage average, which is just over 60 damage average, or a straight up kill on anything it does max damage to.
If you want to be really savage, tag Fell Drain onto PW: Pain. Or, for those egregiously cruel type, Fell Animate. In fact, add Echoing Spell to that and just "convert" whole villages with one day's spell slots.
And that's before metamagic reduction abuse for those two. I'd wonder if someone could figure out a way to make Dracolexi abusive with that, as 3 levels gets you PW: Pain as a 0-level spell at the cost of a casting level.
Or, if you want to finish solo, a bit of empowered PW: Pain followed by a PW: Disable followed by ordinary harsh language, and you can take out the boss before the rest of the party hacks through the grunts.
PW: Nauseate is great, but also look at 1st level PW: Fatigue. Auto-fatigue if you get past SR, then auto-exhausted if already fatigued. And hey, how about a little PW: Weaken right after that? Yeah, -6 Str from exhausted, -2 Str from PW: Weaken, and Str dump-stated wizards are laying on the floor helpless. Even the BDF will be looking a tad queasy, or use PW: Maladroit for archers or finesse fighters or roguish types.
PW: Deafen is pretty much "stay at medium range or take a 20% spell failure rate" for arcane casters up to 10th level, and even divine casters had best be careful.
If your party is full of flankers, PW: Distract at just the right time should kill pretty near anything without SR up to a decent level.
The thing is, if you want to go the full Evil DM, remember that for a mere 100 gp your kobolds can get a 1st level spell as a spell-like ability 1/day with the Draconic Rite of Passage. Between PW: Pain and PW: Fatigue the players will go through PCs on a continuing basis.
For all of them, I think one of the better elements is that by the text, the target does not have to hear the power word spoken. So aside from outright RAW abuse like Silent Power Words, how about just slap some sovereign glue on your whisper gnome, have the BDF fastball special him onto the enemy caster, the gnome invokes his silence, and you "talk" the caster to death as he tries to escape in silence.
I agree though, the higher level ones are less than spectacular. It is those low-level ones that are full of juicy abuse potential.
So is this worth some additional discussion?
Are there other ridiculous combos that haven't occurred to me to make Power Words killers up to 6th level PW: Nauseate?