Problem is Kylo is he is not a scary villain. He is more of straw man for the heroin.
Let's compare him to Darth Vader. Vader is strong, powerful, smart, unemotional, people fear him and he is intimidating. Vader is cold and efficient. You never see him without his mask until Luke takes it off. This guy doesn't have a problem with killing his own underlings for failing him. He is driven and wants revenge. He will go to any length to get what he wants. He is villain with teeth and willing to use them on everyone. The hero constantly gets beat by him or at least barely escapes. He is scary.
Kylo was great until he tried to question Poe. Poe starts making fun of him right off the bat. Poe would instantly die if he did that to Vader. Why does he accept snarky comments unchallenged? Kylo has temper tantrums. He makes dumb command decisions. He punishes people for logical questions. He is openly conflicted with the path he wants to take. He keeps taking his mask off destroying any mystery about him. He broods over his choices and hesitates on his actions. Kylo is weak and unsure what he wants. He gets beat way too easy by someone that never held a lightsaber before. In fact, every time he goes against the heroes, he loses. He is an emotional emo man child desperately pretending to be something he isn't. He is unable to commit to any course of action. He isn't powerful and unstoppable. He is a villain without teeth. What good is a hero when the villain is weak and easily stopped?
Vader would have Rey for lunch.