I play lots of characters ... I love my monk, he was lots of fun to level, stunning fist and high AC was a great combination. I looked forward to quivering palm at level 15 and, once it's ki cost was reduced, found it very good situationally (although it does seem like he rolls a d1 to hit with it sometimes). The problem I have is I can't boost it's DC to a level where it's useful in end game content. It works ok in mod8 but with mod9 going to shavarath I'm worried it'll be next to useless again.
Now I'm leveling a rogue and having lots of fun with assassinate and I fear the same thing will happen, he'll hit shroud/sub content and be unable to use it anymore so I decided to compare the DCs of various other attacks which require a fortitude save and came up with the following:
Save Source: Base/Specced/Peak fail result (restrictions)
Sorc/Wiz Finger/PK: 32/35/36 death (spellpoints, spell resistance, 2s cooldown, 1s alternating)
Barb/Fighter Stunning Blow: 34/40/44 auto-crit (hit, 15s cooldown)
Monk Stunning Fist/Quivering Palm: 26/28/30 auto-crit/death (ki cost, hit, 6s cooldown, 3s alternating)
Rogue Assassinate: 30/32/34 death (stealth, sneak attack, hit, confirm, 15s cooldown)
Base save number represents something that can be achieved with minimal effort towards increasing the DC.
Specced save number is what you should be able to achieve if you build specifically for this spell/attack.
Peak save number is what you might achieve under ideal circumstances (clickies, shroud exceptional stats, short/mid term buffs, sacrificing other build elements)
Of course these numbers aren't perfect, for instance you could probably build a drow rogue with maxed int who relies on sneak attack/flanking bonus to hit and get his assassinate DC up to 38-40.
Some points of interest:
1) My barbarian with a stun DC of 41-43 can stun almost anything.
2) My PK spec sorc with a DC of 35 can PK occasionally in the sub/shroud.
3) My monk with a DC of 28 can maybe stun/kill the mindflayers.
Another point of interest is the barb/sorc's DC comes from the primary stat, boosting it has few drawbacks whereas a rogue/monk sacrifices DPS/to-hit in order to increase the stat the DC is based on.
Some conclusions/assumptions you may or may not agree with:
1) Fort saves were bumped up to prevent casters nuking everything.
2) Stunning Blow/Fist, Quivering Palm and Assassinate don't need limiting further. The long cooldowns, ki cost, hit and/or confirm requirements combined with a moderate fort save are enough.
3) Mod8 went a little way to striking a balance with Enter the Kobold and Monastery of the Scorpion.
Some options/pleas for going forward and mod9:
1) Give us items to boost monk/rogue attack DCs.
2) Use spell resistance instead of fort saves to limit spellcasters in mod9.