I like Critical Hits and Fumbles. The idea that rolling a '20' or a '1' has strong effects livens up games for me, and adds a lot of extra spice to a combat. What I don't like, however, is that they can too often prove fatal for low-level characters. 'I hit myself' for a first-level Fighter means that every time they attack, they have a 1 in 20 chance of committing suicide. Double-damage for a Goblin means that that poor Fighter once again buys the farm. I've seen it tear apart too many games, and cause too many TPKs, so this time, I decided to try something different.
On a '20', a PC has one of two choices. He can either inflict maximum damage with his weapon (not double, as we are simply talking about using the weapon to its maximum effect, rather than some super-blast), or receive a +4 to his next 'to-hit' roll. On a '1', the effect is simple – he cannot take any combat actions next round. He's dropped his weapon, he's ended up out of position, he fell over a log, something – he can take a action, so running away remains an option, but he cannot actually attack anyone.
Then we come to '0' HP. I usually say that if you hit -1, you are dead. End of game. Brutal, harsh, but I think fair. The -10 HP means that a low-level character will have more ability to survive while unconscious than while standing on his feet. Again, I've modified that for my current campaign. There is a 5 HP margin – you die at -6, and -1 to -5 represents unconsciousness. I have introduced a 'maiming' table, however. You get that badly wounded, and there is going to be a consequence. A D30 table, this one, with the middle ten options 'everything is OK'. So far, no PC has died, but a lot of them would be hard to recognise.
So how do you do this? I'm curious how other tables handle this, beyond the 'double damage or hit yourself' idea...