The shield and absorb works great for snipers and all non sorc classes have at least some white damage
Correction : It just works against Snipers, not at all against Sorcerers, and works a bit against some non-Sorc classes (Juggernaut - Marauder - some Mercenaries), and is near useless against the other ones (Powertech - Operatives).
It works against white damage but it's useless against critical damage, why is that?
Because it's supposed to be balanced around the possibility to be either shielded, crit or normal. With equivalent amounts of Shield/Absorb and Crit/Surge, statistically, it's like if the defender wouldn't have any of Shield/Absorb and the attacker any of Crit/Surge. It's just that as a result, the Tank is super spiky when comparing a shielded hit to a critted hit.
That's only when the shielding mechanic is not ignored because the attack is Tech/Force type. And this is the problem. Not shielding a crit is normal (arguable design-wise, but not balance-wise).