A Whirlwind Barbarian build focuses on area of effect damage through an increased critical strike chance and maintaining high levels of fury. This "Diablo 3" build is primarily for large groups and has diminishing returns on single mobs. Boss battles are easily won with the Whirlwind Barbarian, which makes rushing through nightmare or normal mode possible.
The key skills involved in this build are Battle Rage, Sprint and Whirlwind.
Battle Rage helps build fury, plus extra damage and critical strike chance; use the Into the Fray rune to enhance this further. Sprint allows the creation of damage-over-time tornadoes that aid in building fury, while the rune, Run Like the Wind, enhances these effects. Of course, Whirlwind is the gem of the build. It deals area damage that can crit; plus, it provides the benefit of moving through monsters while it's active. When Whirlwind is coupled with the rune Hurricane, the mobility and tornado generation of Sprint is increased.
Focus on buffing critical strike chance. Critical strikes are what make this build stand out, and the target should be 50 percent or higher after buffing. Boost critical damage to give each strike more impact, and increase attack speed to increase the damage output.
Gear should focus on critical strike damage and chance, with vitality as a secondary focus.