From Diablo Wiki
Spin2Win (or S2W) is the nickname for a cookie cutter Barbarian build. It was the most powerful and popular build during Diablo 3 vanilla and was popularized by Alkaizer, the first Paragon 100 character.
All of the skills in this build still function in D3v2 and Reaper of Souls, but the overall build is much less effective. Sprint and Whirlwind still work fine, but the support skills that formed the backbone of this build were nerfed, in the opinion of most players.
- The tornadoes created by Whirlwind and Run Like the Wind have much lower proc rates.
- Battle Rage: Into the Fray no longer produces massive amounts of Fury.
- Wrath of the Berserker can no longer be extended in duration by earning huge amounts of Fury.
These changes mean that while players can still enable all the skills in this build, it's much less effective than it was in the old days, and is no longer a popular play style.
 Build Details
The following refers to the build when it worked very well, during 2012 and 2013 in Diablo 3 vanilla.
The particulars of the build varied from player to player, but the essential core was the use of Sprint: Run Like the Wind at the same time as Whirlwind. Sprint provided a movement speed buff to Whirlwind, and emitted tornadoes along with those created by Whirlwind. These tornadoes proc'ed with Battle Rage: Into the Fray buff to generate huge amounts of Fury. These enabled the Barbarian to use Sprint and WW non-stop, and with good enough gear and very rapid movement between groups of monsters, a Barb could remain in the Wrath of the Berserker form full time, granting huge damage bonuses, as well as additional movement speed and immunity to CC] effects.
 Example Spin2Win Build
A typical example of the build can be seen below:
The LMB skill varies by personal preference, as do the passives, mostly depending on the quality of gear. Players without top quality gear (or who were playing on higher difficulty levels) needed to use the passives to improve their Fury generation, Life Steal, resistances, defense, etc. Characters in better gear tended to focus more on increasing their DPS.
 An Overpowered Build?
Most players felt this build was overpowered, as it had no real weaknesses and was not very expensive to equip or complicated to operate. With it Barbarians could move very quickly, kill rapidly, generate almost infinite resource, and ignore almost all enemy attacks. It was a powerful build for farming, but could also be used for high MP grinding, such as key runs, with high end equipment.
Blizzard clearly agreed with the player consensus, as this build was nerfed to non-functionality by the numerous skill changes implemented in Diablo 3 version 2.