But they are horribly unfair to Players. Even if the Players enjoy the tables they will never escape the ultimate, grim conclusion of death at the hands of a crit table. All things being equal, there is only 1 PC and an endless amount of NPC's. After a while a long-lived hero dying at the hands of a rando critical from the town guard will grate on everybody's senses of dramatic play. Brand new adventurer, no problem, take that axe to the stomach and bleed out like a, a... hero! But the PC which has achieved great success at great cost, a meaningless death annoys me.
Another inescapable fact was the more PCs engaged in mortal combat the more they cement the inevitable. The act of a fighter fighting becomes a sub-optimal play.
My first stop on the train of reflection and thought was to appreciate the original parameters of the first critical hit and dramatic fumble mechanism in a rpg. A natural 1 is always a miss, and a natural 20 is always a hit. No bonus to damage, no increased penalties beyond the miss, kind of captures all the back and forth thinking I have on crits in a simple solution. But damn it, I love random, descriptive killer hits during combat when luck has prevailed in favor of the PCs! I have, in the past, modified tables in all sorts of ways to minimize the chance of an inappropriate crit coming up in the course of regular play. Qualifying the critical was an obvious choice for me, but in the end I came back to the facts of a closed system; just delaying the inevitable. A lucky shot which blows apart years of quality play.
So my current solution is Critical Hits are only for Players. Only the PCs get those extra rolls on a critical hit table when the score that magic number. No NPC gets anything more than just a hit, no matter what combination of rare results they pile up. Same for Dramatic Fumbles, NPCs only. The dramatic fumble always makes an exciting turn in the events of a combat, and quick players will grab onto additional environmental "things" and make something interesting out of the action. And I don't think this is tilting things in the PCs favor all that much. The PC is always exposed to death during a game session. Eventually it will come when all is reduced to a single role. In a closed system with endless amounts of time the unwanted event will come about no matter how small a chance, and come often! So the PCs are going up a steep climb anyways. Why not make it vivid and colorful along the way?