“If the initial roll falls in the Critical Hit range of a weapon and is a hit (a natural 20 is always a hit), then a critical hit has been done to the target. Maximum damage (including Str mod) for the weapon is done to the target.
Roll an attack again. If the second roll is a hit (not a critical hit, just a hit), roll for damage and add the damage roll (including Str mod) to the maximum damage done because of the critical hit. If the roll is a miss, nothing is added to the maximum damage of the first roll.
If the second roll is a Critical Hit, continue the process until a normal hit or a miss is rolled.”
The X2 rule that many of us have used in the past has simplicity on its side but if you roll a low number for damage, it’s hard to call that “critical”. With the d20 Modern rule, it’s possible to roll a natural 20 and not do any extra damage at all. Add a low roll for damage on that and it really takes the oomph out of rolling a 20.
With my variation (which is still open to discussion), rolling a crit will do max damage at the very list and goes up to infinity from there.
On the infinity aspect, from the DM side, I am going to limit the damage that can be done to PCs. The limit will be max damage plus one roll for damage (if the second roll is a hit), regardless of attack rolls. The way luck goes on these things, I could just see me implementing this rule, attacking for a drake the very first time, rolling three nat 20s in a row, and killing one of you in one bite. No fun. You guys are the heroes and get to do the heroic things.