Isn't its purpose to draw the target's aggro back to the tank? Yeah, it also supposedly drops the critical attack of the target....
It has a nice application for the DA's panther summon to 'take back' aggro from the target in PvE.
I don't know if it does anything with actually decreasing crits in PvP--my guess is it would be so random (Korean randomness that is) that in landing, only one time in 2000 hits would it actually reduce anything on another player's stats. I also don't know if it could actually retarget in PvP. Again, my guess would be no.
It does draw target's attention in PvE (at least away from summon--even when summon is doing more damage to the target) a fair amount of the time. And of course over-hit is possible.
It seems to deliver about 25% more power when it lands than a regular hit to a mob. You hit for 200 damage, you'll see judgement do 250-260 or so on that same mob.
When Judgement lands, it does what it says it does. No random factor at all. Ever since they added the Stigma of Shillen style debuff, it's even better for melee classes. Especially for low damage tanks.
At any rate, it's one of (if not the only) decent attack skills a dark tank has. When you fight those annoying high evasion classes, you're going to need it. Especially as over-powered Shield Stun doesn't actually do any damage!
a good tank in mass pvp would root melee, hate nukers and lower the critrate/dmg of daggers/archers of the opposing force, so that they do less dmg to your force...