Every great superhero needs at least one great supervillain. The better the bad guy, the more invested we are in the outcome and the more the story gets its hooks into us.
That’s why a great villain is so important... but what actually makes a great villain? It’s not whether they can beat the good guys, or even come close - plot convention generally requires the antagonist to be taken out in the final act regardless of how awesome they are (or aren’t).
No, it’s some compelling combination of factors: something that intrigues you, makes you keep coming back to see what happens next. They could have a fascinating relationship or dynamic with our hero, or they could have a unique look or power set. Their appeal could lie in the story they’re a part of, or (in the case of villains on the stage or screen) simply in the sheer brilliance of the performance.
The TV shows that make up the Arrowverse have had their fair share of damp squibs and missed opportunities over the last seven years, presenting forgettable takes on classic comic book moustache-twirlers like Ra’s al Ghul, The Thinker and Vandal Savage. But there have been far more dreaded devils than dreadful douchebags in the Arrowverse to date...