My friends and I usually like games where crits have at least a chance of sudden death. In our worlds, the stable boy needs at least some sort of shot against the Dark Knight, even if it's the slimmest of hopes (call it the Rolemaster School of Crits, I guess).
We've played a lot of games centered around a d20 combat roll (from D&D to Palladium Fantasy) where a crit does 2-3x damage at best. Our quick n' dirty solution in days past was to roll a d6 after any crit to determine the damage multiplier the critical hit did:
Critical d6 Multiplier Roll
1-2: Double Damage
3: Triple Damage
4: Quadruple Damage
5: Quintuple Damage
6: Sextuple Damage
Besides the fun of saying "Quintuple Damage!" at the gaming table (seriously, try it sometime), this often sped combat up, made it more lethal, and added an element of luck to the whole thing that we enjoyed. It let your 1st-level fighter have a snowball's chance against that evil warlord without letting get too hopeful. Just a silly little houserule, but one we enjoyed. If you don't have a critical hit deck, a book of charts, or a system that's doing critical hits how you'd like, but you don't want to put too much thought into it, you might give it a whirl.