SPOILERS FOR STAR WARS: THE FORCE AWAKENS BELOW
Is Kylo Ren a good at his job at being bad? That depends on if you judge him by his ability to construct a lightsaber.
When we saw Star Wars: The Force Awakens, we saw Kylo wielded a sparking, jagged saber. I had assumed it was a deliberate choice on J.J. Abrams' part, perhaps an update to the saber we’ve become familiar with since 1977. But no. Kylo’s saber, it seems, is flawed in multiple ways.
According to Star Wars: The Force Awakens Visual Dictionary:
“Though Kylo's weapon evokes an ancient feel, its components are modern. Its crude appearance suggests construction by an inexperienced hand. The stressed crystal barely contains the power of the weapon, necessitating lateral plasma vents that become the crossguard quillons.”
And the reason his saber has a “ragged, unstable appearance” is because Kylo constructed it with a cracked kyber crystal. Whoa.
The man formerly known as Ben Solo killed the Jedi-in-training with that very saber and sent Luke Skywalker into hiding. Although the Visual Dictionary does not state it, perhaps Kylo attacked the Jedi before his lightsaber training was complete.
Whether or not Kylo was the best Sith ever (because he made a lightsaber that killed the budding Jedi Order from substandard parts) or the worst Sith ever (because the final product wasn’t smooth and clean) ... depends on a certain point of view.
But when it comes to the ability to be a villain, judge him not by his lightsaber. Judge him by the fact that he had Force Pull and Force Choke down -- at the same time.