Crueler Criticals
Normally, when you score a critical hit, you roll the damage dice twice and add your modifier once. For instance, if you are wielding a weapon that deals 1d8 kinetic damage and is governed by Strength, on a critical hit you deal 2d8 + your Strength modifier kinetic damage. Sometimes, poor rolls lead to you doing less damage on a critical hit than a normal hit. For instance, you might roll two 1's on your 2d8, which with your +3 Strength modifier is only 5 damage. This feels lackluster.
With this rule, instead of rolling the damage dice twice, you instead maximize the damage once and then roll the second die. So, using the above example, instead of rolling 2d8 and adding your Strength modifier, you instead roll 1d8, add 8 for the maximum die roll, and then add your Strength modifier. This will make critical hits feel more impactful.
Why I Recommend This Rule
As indicated above, this variant rule helps make crits more impactful, but it's a double-edged sword, since it can make damage against player's spike, too.