I'm not a fan of limb severing silliness but I do enjoy using an exceptionally bad miss table in games where there are critical hits. It kind of balances the scale when there is as much dread of rolling a 1 as there is excitement in rolling a 20. I do believe the scale of payoff/ penalty to crtical hits and misses should be in proportion to one another. If the best result of a critical hit is maximum regular damage then a fumble result should never produce anything nastier than that.
Whats the appeal of critical hits in an abstract combat system where "damage" from a hit might represent energy expended by the defender rather than an actual hit?
I think that critical hits in any system are really just an excuse for a little "gamism" that comes in when you roll one and people say, "Sweet!" Roleplaying games without critical hits or some other exponentially better result when X happens (in this case, a natural 20) may suffer for it, because you don't have that moment in the game where the tides turn solely based on the roll of the dice.
I suspect it's similar to playing Texas Hold 'Em and getting bullets in your hand, and an Ace on the flop. I don't know about anyone else, but I find it REAL HARD to keep the poker face on at that moment. You just know you're the shizzle then and there, even if it does play out exactly like you want it to. For that instant, you're finally "cool."
;-P
I hope this didn't come up and I missed it, but what's the appeal of adding firearms in D&D?