Isn't Order 666 when all the Clones start headbanging to death metal?

Order 66 is different though, and hardly single handed. The entire thing is a giant mechanism that's taken decades to prepare. It's an incredibly intricate plan which involves:
* breeding an army of clones that are genetically programmed to take orders without question;
* integrating the Jedi into this army, allowing the Clones and Jedi to build a deep bond; wage a war for several years where the Clones are continually following battle orders under the Jedi's command - thus the Jedi are acclimatised to how the Force feels like whenever the Clones shoot someone;
* activating Order 66, where the Clones are just following yet another order to shoot someone. There is a trigger in the Force, but the Jedi have been feeling it for years during the Clone Wars, and also Order 66 is ordered in the middle of battle, so the Force hasn't even had a chance to "ebb" (thus allowing the Jedi to be more sensitive to any fluctuations). This allows the Clones to take the Jedi by complete surprise.
The whole thing works like a magic trick where you misdirect the audience in order to successfully perform an illusion. Palpatine set up the Clone Wars as one gargantuan misdirection, so that he could destroy the Jedi Order and topple the Republic (thus establishing the Empire). Nobody saw it coming because they were all deceived.