Like Rosveen stated, Critical Hits only uses a weapon's base damage as a point of reference making the damage very negligible if you have upgraded the weapon in any way or have enchantments to enhance your weapon damage.
If I understand the numbers correctly, Critical Hits inflict half the base damage of the weapon you're using. So if the base damage of the weapon you're using is 14, then you'd inflict 14+7 = 21. The Critical Hit becomes extremely negligible once 14 becomes much higher through smithing or enchantments. You're not going to notice the Critical Hit when the math is something like 500 + 7 = 507. The Critical Hit is dealing less than 2% of the damage you normally deal with your weapon.
I've come to the conclusion that Critical Hits will only be useful if they use your weapon's current damage as a point of reference as opposed to using a weapon's base damage as a point of reference. Same with the bleeding damage perks that work in a similar fashion.
It sounds like Critical hits should have taken further influence from Fallout (1 & 2). In those, Criticals can ignore armor, knock down or knock unconscious, blind, maim, or kill instantly... and potentially do hundreds of hitpoint damage either way.