Uller
Adventurer
*Critical hits apply maximum damage on the damage die, and then you roll the dice again. So, your minimum crit damage increases, but the max remains the same, and you never have a crit that does less than the average non-crit.
The way we do it is max damage plus ONE damage die of the attacker's choice. This makes crits good, but not too good. If do max damage plus roll all the dice, Rogues and Paladins are going to do crazy amounts of damage.
So if you do 1d8+3 piercing plus 1d8 fire damage plus 2d6 sneak attack damage (which would be piercing or fire damage) and you roll a crit then you do 11 piercing plus 8 fire plus 12 (fire or piercing) plus 1d8 (fire or piercing. This makes an attack that normally averages 19 damage (min 7, max 31) crit for 31 plus 1d8 (average 35.5 min 32 max 39). If you were to max plus roll ALL dice in this situation you'd do 31 plus 2d8 plus 2d6 or average 47, min 35, max 59.
IIRC this was the original crit rule in D&D next.
Edit: Math