So, in my campaign, our half-orc barbarian (with 18 strength and a 1d12 damage great axe at level 1) has the feat Great Weapon Master, which states that every time he crits or kills something with a great weapon, he can make a bonus attack. We're fighting Kobolds. With 5 hp. It was a bloodbath. In 3 fights he, alone, killed about 17 kobolds.