Star Wars has revealed why the First Order is even worse than the Empire. When Lucasfilm launched the sequel trilogy in 2015, viewers were taken aback that the villains were essentially the Empire 2.0. The First Order wore the same uniforms, they had the same love of superweapons, and their armada was composed of Star Destroyers to boot.
From an out-of-universe perspective, this was because Lucasfilm felt they needed to appeal to nostalgia to persuade fans Star Wars was safe in their hands. Little by little, the in-universe rationale has been provided; the First Order was established by Imperial loyalists who had survived the fall of the Empire and regrouped in the Unknown Regions. Star Wars: The Rise of Skywalker further revealed the First Order was the brainchild of the Emperor himself, who had survived his death in Return of the Jedi. This explained why even the aesthetics were so similar. Still, Alexander Freed's recent tie-in novel Shadow Fall has revealed the First Order should be viewed as far worse than the Empire.
After his death, Palpatine sent out Sentinel droids to convey instructions to his most loyal Imperials. He ordered them to begin Operation Cinder, a scorched-earth policy that wreaked havoc across the galaxy. Countless worlds were razed, with the New Republic desperately attempting to prevent numerous acts of genocide. As horrific as this may be, it was a masterstroke on Palpatine's part, fulfilling many purposes at once. One of the most sinister was - from the Emperor's perspective - to refine the Empire down to its most loyal soldiers and commanders. After Operation Cinder, the only ones left would be those who had participated in unspeakable horrors; anyone with a conscience would have defected. And these fanatical, immoral loyalists were the ones who founded the First Order.
In truth, Palpatine had probably been "refining" the Empire in this way since the destruction of Alderaan in the original Star Wars. As revealed in Claudia Gray's Lost Stars, most Imperials had believed the Tarkin Doctrine, that the Death Star would cause such fear across the galaxy that it would never be used. Then it was fired; on Jedha, Scarif, and finally on Alderaan. The last case in particular shook many Imperials to the core, causing them to defect. Still, even after Alderaan they had told themselves the Empire was flawed but still a force for good. They had considered the Death Star to be Tarkin's folly, and assumed it would never be repeated. Then they learned a second Death Star had been constructed in the Endor system. The Second Death Star's mere existence caused more defections than its destruction and even the Emperor's death.
But it is one thing to be part of a brutal regime; it is another to perpetrate that brutality on an insane Emperor's orders. Operation Cinder forced every Imperial soldier and commander to decide whether or not to obey their Emperor, even to the point of committing genocide. When Operation Cinder was over, any good men left had been corrupted beyond redemption because of the horrors they had taken part in.