In games that I have played, critical hits a great and all but are sometimes over shadowed by regular hits. For example a regular hit with a great sword with a modifier of +5 can do up to 17 damage, where a critical hit could do 29 damage, however in some cases a critical hit would only do 9 and the next hit would do 15. In the last game I played the DM had a house rule where if we did a critical hit the initial damage would be auto maxed and then we roll the critical damage, i.e. initial damage from the previous example would be the 17, and then add 2D6 on top of that. So I was wondering what other house rules for critical hits are used?

We use the same system you do.

Your approach is fair as long as the monsters get the same benefit OR the DM moderately boosts their hp.

I always set Monster HP to Max, so, yeah….

We used to do this, but it gets quite deadly when used by some monsters. Giants, for example.

My current rule is this: When you crit, once you roll damage you can change the value of one die to its maximum value. Starting at 11, you can max two dice. This is pretty equivalent to OP's method at low levels, but doesn't get crazy at high levels.

For monsters I roll Crits as normal, we only use the modified Crits for PCs.

I have a table with certain conditions on it that I sometimes roll on or have players roll on.

Basically it is the same as the default rules, and does apply to monsters, but on a critical, i have a table of Conditions that can also be added to it if the combat could use some spicing up.

We've only usedit a few times, since it is a fairly new addition -- it can rapidly change the feel and flow of the game.

It doesn't have any "instakill" things or massive damage boosts. It is conditions -- so like "that critical strike blinded them in one eye" would be a critical hit result, but so would "you hit them so hard they are stunned for a round".

Befuddled, Choking, Coughing, Frightened, Horrified, Immobilized, Incapacitated, maddened, Numbed, Sightless, Soundless, Stunned, Stupefied, Unconscious

Those are the conditions on the table. The maddened one is like a mini-rage, targeted on the one who hurt them, on the basis of some people lose their stuff. It gives the struck person disadvantage but no bonuses to damage.

I also have a Fumble version, but it doesn't do much except interfere with the next turn (dropped your sword, weapon is stuck, trip and stumble, no movement actio, etc).