Thanks
FF
I almost never use VATS, only thing I've noticed is that in 1st person where you land the hits seems to matter. Shoot them in the head they die "sooner" Legs they might trip and arms they could drop their weapon.
I don't think there are random crits, at least without some perk I don't have yet.
Why?
When I look at my combat stats, I see that "Sneak Attacks" and "Crits" both have the same value. i.e, the only crits I've gotten were because of sneak attacks.
I've received several critical hit pops ups outside of VATs, only noticed them today, so no idea if it's a bug. But they were there.