Too often in D&D, combat becomes a mere battle of attrition to see which side can bring their enemy to zero hit points first. And that's fine. Hit points are how we measure life and death in D&D. But that can get boring, and I think it ignores the tactical dimension of combat.

Maybe critical hits could offer more options than simply doing extra damage. What if critical hits enabled you to forego that extra damage to instead gain a tactical advantage over your enemy? While combat arms classes have obvious training and experience with such maneuvers, it may seem counter-intuitive to grant tactical options to people like wizards and clerics and such. But I contend that anyone who chooses the adventuring lifestyle will, before long, experience enough combat to be capable of such options. Granted, the typical wizard receives little or no combat training in their arcane education, but the "typical wizard" also spends their life as a sage or a professor or a researcher, not delving ancient ruins and fighting monsters. The adventuring wizard is definitely atypical. 

So... while doing extra damage is always nice, sometimes other options can give the party as a whole a greater chance of success in an encounter. Here is my proposal:

When you score a critical hit against a target, you may choose to do the usual extra damage, or you may choose instead to do just regular damage AND employ any one of the following options:

1. You may Disengage from the target and move up to ten feet (without provoking attacks of opportunity).

2. You may force the target to make a Strength saving throw or be knocked prone. DC is 10 plus half the damage dealt.

3. The target is pushed ten feet away from you.

4. The target's speed is cut in half until the end of its next turn.

5. The target has disadvantage on Dexterity checks and saving throws until the end of its next turn.

6. The target is blinded until the end of its next turn.

Of course there will be certain limitations placed on some of these options, according to the mechanics of how these effects are achieved. As explained next:

1. As you strike you feint or distract the target, giving you an opening to retreat. This would not work when fighting a crowd or a swarm.
2. You strike the target's legs, throwing it off balance. This would not work against a creature that doesn't stand (like an Air Elemental) or against a creature that occupies the floor (like the lovable Gelatinous Cube).
3. Pushing a target may be limited to creatures no more than one size category bigger than you. You can't push a Purple Worm.
4. And so on . . . 

Pros:

1. This would add a new tactical dimension to battle which would make it more realistic and textured.
2. This would allow players to think and act as a team, considering not just how much damage they can do, but how they can help their teammates gain a greater advantage.
3. This would give the players more options, which in my opinion is almost always good.

Cons:

1. Enemies would be able to use these options against the players as well!
2. By adding one more decision to a combat round you risk slowing down a combat system that already takes too long to resolve. 
3. The traditionally combat-oriented classes may feel encroached upon if suddenly everyone can use tactical combat options.

Solutions:

1. Perhaps this new option should only be made available to the traditional combat classes - barbarians, fighters, rangers, and maybe rogues.
2. Perhaps this new option should be made available as a Feat, so if you want it you have to spend an ASI to get it.
3. Perhaps we should just stick with the existing rules for critical hits and ignore the ramblings of some random dude on the internet.

So, why would someone voluntarily forego doing extra damage???

Let's say you're a fighter swinging a longsword. On a hit your damage is 1d8 + your Str mod. On a crit you do an additional 1d8 damage. But you're low on health and the enemy is next in initiative, and he is almost certainly going to kill you. Unless you're absolutely certain that your extra 1d8 damage will kill the target, wouldn't it be wiser to do regular damage and blind the target, giving it disadvantage on its attacks against you? The smart move is to live to fight another round.

Or maybe the enemy isn't next in initiative. Maybe your friend the wizard is, and you just know the wizard has got a Lightning Bolt on deck. If you choose to forego that extra 1d8 damage you could instead push your enemy off balance, giving it disadvantage on its Dex save against that Lightning Bolt, and greatly increasing the chances that it takes full damage rather than just half. You'd do less damage as an individual but you'd be doing much more damage as part of a team!

Or maybe you're a rogue attacking with advantage and you've got that sweet sweet +7d6 Sneak Attack on your side. If you roll a crit, take it! Take that extra damage! That's the smart move!

Anyway, that's just something that's been rumbling around in the old noodle today. Food for thought. Nothing set in stone. Just exploring options. Feel free to ignore or pontificate as you wish. 

This is very cool. 

Thanks, bud!