I saw them in '77 at the height of their early fame. The "Destroyer" tour. I was 17. As a fan of comic books, I thought the show was a blast! And yes, I liked the music, too! I bought "Kiss Alive" and "Destroyer" and played them loud...
I think I eventually outgrew their music, and/or my tastes simply changed. Never bought an album after "Destroyer". But if I hear "Detroit Rock City" or "God of Thunder" on the radio, I will definitely turn it up!
The make-up, characters, etc., was/is marketing genius. Period. As
@Boneman said they would not have lasted this long without talent, but the whole marketing "universe" they created around the characters, etc., was a brilliant business strategy. They took the whole Beatlemania merchandise phenomenon and multiplied it times 10. And it is paying off for them once again.