Kylo Ren (which incidentally is a stupid and terrible name) was only a half-decent villain while he kept his mask on. Once he took the mask off, it was all over. Any scariness or credibility he had went right out the window once his whiny prequel-Anakin true persona was revealed.
Based on your post, you and I obviously have very different opinions of this movie, and that’s cool - each to their own. But your one point I’ve highlighted above really jumped out at me because I felt the complete opposite. As i’ve said, I’d avoided all spoilers, so all I’d really seen was a few promo shots of a guy in a Vader-esque mask and I was like ‘why have ripped off Vader?’ but when I saw his face (young, vulnerable, and not at all vader-like), I began to understand his motivation, his angst, his self-doubt, his grand-daddy issues… that’s when he became really interesting to me. In short, when he became more human*.
I also thought the notion of a character being tempted by the light side and fighting to resist was interesting.
*I know he’s not actually human 😉