Berserkers can use their melee weapons to block incoming attacks, allowing them to keep ZEDs at bay when things get hairy.
All Berserkers specialize in close combat weaponry, but their perk choices let them focus on either being a damage resistant dreadnaught who refuses to go down, or a fleet-footed skirmisher dishing out violence by the truckload. The Berserker is the shield that keeps ZEDs away from your squad by cutting them down like an overclocked lawnmower.