Not gonna lie, I've been into a lot of older anime these days and out of all of them, this is one of them that's somewhat tolerable (I think since it breaks the stereotype of the clean-cut, good-looking main male character. Nice to finally get some variety). Also, maybe it appeals to the romantic in me, but I do find it kind of a cute concept that a demon goes out of his way to save humanity all for the sake of one woman. The only thing I find super silly is the fact that he's like "I must defeat this evil demon lord and the restof the Demon Tribe!"
"Hmm, did you say something?"
"...nope."
Or he basically morphs right in front of them and they're like "Did you just see Devilman??"
It's ridiculous to the point that it's just amusing.