Everyone knows that blanket immunities are bad. But, how to change?
Make each mob take a certain number of vorpal strikes. Make each one different so we get to discover the details of the mechanic as we kill.
Vorpal immune 6-man trash = about 10 vorpals kills the mob, some less, some more
Vorpal immune 12-man trash = about 20
Vorpal immune 6-man red names = 30-60
Raid bosses = about 100
Epic Raid bosses = about 200
It would be really fun to be about done taking eDQ down and some assassin III rogue or pale master get a lucky vorpal. I'm including all instant death effects here.
Devs could even write a bunch of fun descriptions to make watching the Z button window useful, while still not knowing the exact number of vorps left. Would be fun with charged gauntlets on too, so you can shout out whenever you get a vorp, in case the group knows how many vorps a certain mob/boss takes and is keeping track, before asking the casters to unleash a bunch of fingers/wails/fods/destructions.
I don't want to go back to the pre-epic vorpal/insta-death domination, I just want it to be an interesting mechanic still.