I know purists would crucify me but I always thought Kirby was over rated. I like his stuff and his style was unique. But art is subjective n that's just the way I see it. Sometimes I think it's just the cool thing to say how great Kirby was so everyone jumps on the band wagon.
I have some very old original drawings signed by buscema btw
Kirby's stuff in the 40's was remarkably influential on later comics; he established a lot of the theories for layout and pacing that became absolutely ubiquitous. In that regard he was instrumental in taking comic books away from their strip roots and toward their own thing. He created the very language of comics, and co-created more characters, concepts and worlds than any creator before or since, Kirby is a comics GOD.
Love Buscema btw, but even he went to Kirby for tips and knowledge on how to make the heroes "pop"! Buscema hated to draw superheroes, Spider-man was his least favorite. He was all about fantasy, that's why he worked on Conan for so many years...