Alternate Critical Rule

[Rurik]

I have been using max weapon damage plus double damage bonus for crushing weapons. Seems to work pretty well. Increased chance of knockback comes from increased damage if the weilder is big and strong.

You could do Max DB + Rolled DB for a bit more bite.

 

[Deleriad]

Well I use, fwiw,
Impales: RAW (max weapon plus impale)
Slash: roll weapon damage again and add (not damage mod)
Crush: roll damage mod again and add (bad news for ducks)

It's simple and gamey (big things use clubs for the damage modifier) though perhaps lacking in simulation; afaik, concussive damage can be very dangerous through armour due to internal bleeding.

Mind you, I also use a system where it is possible to gain multiple crits so I tend to use the above as the "default" and then give other additional critical options:
choose location (all types), ignore one type of armour (magic, natural, manufactured)
Thrusting: auto-remove the weapon causing damage
Slashing: location bleeds (if not otherwise bleeding)
Crushing: +10 pts of effective damage for calculating knockback.

So if someone with a mace got 3 criticals then he could choose to roll damage modifier an additional 3 times and add them all or choose
+10 knockback, choose a location and ignore worn armor ("fore!!!") and so on.