At around 22:20 of the video, Gould calls Mozart's early sonatas, concertos, symphonies incredible in their inventiveness, and says that he loves them. I don't think Gould really "hated" Mozart as some people today claim. It seems that he only didn't like what he perceived as "mannerisms and banality" in late Mozart, contrary to the claims of some people who try to make it seem like he hated Mozart's entire oeuvre.
In this respect, he's kind of like the critic David C F Wright, who said "there is probably no greater composer than Beethoven", but still had certain reservations for his late works.
Likewise in other composers, he had strong personal opinions on what he liked or disliked :
"I personally think that a lot of of the fugues in the Well tempered clavier are better off without their attending preludes and vice-versa."
"I don't ever expect to persuade you of the pomposity of the fifth symphony, or the banality of the violin concerto or the empty rhetoric of the Appassionata sonata"
"'a monstrosity,' the harmony 'wanders all over the lot'" (on Bach's chromatic fantasie)
"For me, the 'Grosse Fuge' is not only the greatest work Beethoven ever wrote but just about the most astonishing piece in musical literature."