BioWare Blog: Enemy Defenses in Mass Effect 2

Mass Effect 2 lead combat designer Christina Norman has penned a new blog entry that breaks down the three different defense types our adversaries will be able to utilize in the RPG/shooter sequel.
Shields: The most common enemy defense is the kinetic barrier, or shield. Shields are effective at blocking most powers, but are vulnerable to rapid-fire weapons like submachine guns and assault rifles. Shotguns are also effective as they launch many projectiles with each blast. The best way of getting rid of shields is using disruptor ammo, or the engineer's overload power.

Armor: While most enemies will wear light tactical armor, only enemies wearing the heaviest or most technologically advanced armor will have an armor defense. Armor is effective at blocking most powers, but is vulnerable to hard-hitting weapons like sniper rifles and heavy pistols. The best way of breaking through enemy armor is using incendiary ammo, incinerate, or warp.

Barrier: Only biotic enemies like vanguards can generate defensive biotic barriers. Like shields, barriers block most powers, but are vulnerable to rapid-fire weapons. The best way of getting rid of a defensive barrier is the warp power, but the soldier's concussive shot is also quite effective.