In my upcoming campaign, I'm trying something new on critical hits and fumbles. (Yes, I use fumbles.)
If a player rolls a natural 20 on an attack roll, I won't force the player to roll extra damage. Instead of extra damage, they could choose to do regular damage and perform some kind of stunt. Maybe they do regular damage and disarm their foe? Maybe they do regular damage and knock their opponent prone? Maybe they want to deal regular damage and disengage for free? I bet that nine times out of ten, the player chooses the extra damage. But my hope is that every now and then, when the stars align, something much more memorable happens.
I do the same for critical fumbles. When a player rolls a 1, they miss. But I give them the option to turn that miss into a hit, at a cost: maybe they take a point of exhaustion, maybe they fall prone, or maybe their weapon gains the Broken condition at the end of the attack. Nine times out of ten, I expect the player chooses to just let the attack miss. But I hope that every now and then, when they really need that attack to hit, rolling a nat-1 will feel like an interesting twist of fate.
This house rule will apply to the monsters too, which is why I bring it up in this thread. If a dragon scores a critical hit, it can choose to do double damage per the rules, or it can choose to do regular damage and recharge its breath weapon automatically at the end of the turn. Or it can choose to do regular damage and automatically grapple its target. Or disengage for free. Or knock its target prone. I'll be honest, most of the time that dragon is going to want to take the extra damage...but the exceptions could be very interesting indeed.
My issue isn't with the amount of damage; it's the lack of interesting options. MOAR DAMAMAGE LOLZ!!!1 gets pretty dull after a while.