Aleixandre

 There was a time when Vicente Aleixandre was it. He had won the Nobel, and was being widely translated into English. His poetry fit in with the idea that the most significant Spanish-language poetry was surrealist. In Spain, he was mentor to successive generations. Bousoño, the most influential critic of the time, canonized him, calling one of his weakest postwar works a masterpiece. I myself thought of him as great and would included him in every class and reading list. 

It's not that he isn't an impressive poet, but the perspective has shifted. His poetry doesn't offer as much to criticism any more, at least until someone comes up with something original to say about it. 

I feel the same about Cernuda. There was a certain narrative about why Cernuda was important, and more influential than Lorca himself. But time has not borne that out very well. The side of Cernuda that was influential is not as good. Maybe Alberti is going to be seen as more interesting, ultimately.