As Ragitsu points out, you can find plenty of crit tables in other games. If you really want to include damage to the face you will need to expand upon the core 5e rules to do that. This was true even before the change to crits that they are proposing here.
Nevermind. You just aren't getting what I'm saying. I am FULLY aware 5e doesn't have crit tables or locations. It doesn't matter. The bottom line is, I think not allowing a Firebolt or Guiding Bolt or other attack spells to crit is dumb. "Because they are magic, they can't hit weak spots on enemies. They always hit well-protected areas." Stupid. Makes no sense, and it will not go over well with any players I've ever played with.
Players like crits, and they like crits to mean something. If I tell my players who like to play Warlocks and Wizards that spells no longer crit, they're going to be pretty upset. "What do you mean my Eldritch Blast can't crit now? You mean to tell me that no matter what it will only ever do 1d10 damage? Seriously? Every other type of attack can do increasingly more damage, but my Eldritch Blast can only do 1d10? Even if I roll a Nat 20 I can't even get a potential double damage of 2d10?"
Then the Warlock players are likely going to say, "Guess I'll use regular weapons then instead of spells. Lame. Playing a spellcaster and not even using spells. Time to pull out a quarterstaff. At least with that I can do a crit, AND I can gain some sort of bonus for Dex or Str to increase my minimum damage potential."
And maybe that's why they're doing it. They made Cantrips unlimited and spellcaster players said, "Why do I ever need a weapon anymore? I can cast Firebolt for long range and Shocking Grasp for melee and do just as much damage as a standard weapon, if not more. Plus, I can crit." So WotC said, "Let's make it so spells can't crit. Then maybe spellcasters will use regular weapons again."
I don't know. Either way, I think it doesn't make sense no matter what way I look at it. A standard weapon can hit weak spots, but a hurling bolt of fire can't. Crossbow bolts can find chinks in armor and do more damage, but your Ray of Frost always hits your target square in the well protected areas of their bodies.
