Critical Hit is a stacked gear perk on the Crystalline Gauntlets that bundles four bonuses into one. You get much stronger body shots, front takedowns while spotted, more ammo and faster reloads.
Your body shots hit much harder, so you do not need perfect aim to drop soldiers. You can also run up and take down an enemy from the front after the alarm goes off. On top of that you carry more ammo and reload faster.
Wear the Crystalline Gauntlets. They take your hands slot, so they replace gloves that carry perks like Major Steady Aim or Gadget Sniper.
Yes, for almost any loud build. Few single perks cover this much ground, and it makes the hands slot one of your strongest picks.