As opposed to all the other rolls that were hits but not crits? Those were sloppy and weak? Even a non-crit that deals 3 damage when the fighter is at 2 hp is apparently strong enough to kill a fighter.
Nah, rolling a natural 20 should be a WOO-HOO moment, not a moment where the result is: "Your enemy is badly scratched by your amazing attack."
It's an easy enough problem to solve (especially with modules), but a crit really needs to be something that creates some substantial injury on your enemy, or else it's YAWN.
(While we're at it, we should ditch 4e-style "crits are max damage," since that's a big yawn, too)
Well, at high levels where your example is meaningful, what is a crit with a longsword against a dragon anyway? Running the length of the blade through his foot maybe? I mean you're trying to hit a 60ft-long magical monster with a 3-foot long metal stick.
Sure, when you crit on a goblin you're going to impale the little bugger, lift him off the ground while he's still on your blade, and then pitch the poor thing half-way across the room, or wipe him around on the floor like a mop.
A 5% base chance to crit really isn't that far out there. If we were rolling D% and we had to get 100, now that's a good reason for your longsword to fly from your hands and run itsself headlong through that one soft spot in the dragon, fragment on a rib and explode into metal shrapnel in it's body, instantly killing the dragon.
And critting gets even more meaningless when(using Pathfinder here) a Fighter can crit on a 10 or less.
One thing I feel that 4e did right was that instead of scaling the melee's attack bonus, they scaled the melee's damage. This can easily be accomplished without powers using the same system 3.X used for BAB. Every 4, 5, 6 or whatever increment levels, give every attack made by a guy with a sword do more damage. This makes crits at higher levels more meaningful. When I crit with 1d8+3 str, big deal. When I crit and my attack does 5d8+3str, that's a big deal!