Here’s a partial transcript of what Gould says:
“That example came from Mozart’s piano concerto in C minor, one of the last works he produced in that form, one of only two in a minor key, and perhaps for both those program-noteworthy reasons a work that’s had a rather better press than it deserves, I think, despite its gently swooning melodies its meticulously balanced cadences, despite its stable and architecturally unexceptional form. I’m going to submit it as a good example of why I think Mozart especially in his later years was not a very good ‘composer’, but the italics are squarely on that word composer because Mozart was unquestionably a very great musician — and I’m not being coy when I try to foster that distinction. By the evidence of his contemporaries he was a superlative performer and an improviser of note, by the evidence of our own eyes and ears a resourceful craftsman in the theater, and in all the familiar musical forms of his day an exhilaratingly dependable artist who could knock out a divertamento the way an accounts executive dispatches an interoffice memo, But in a way, that’s his problem: too many of his works sound like inter-office memos. They’re pertinent. They’re often blessed with an engaging sense of humor. They sometimes provide a concise resume of the main points their author wants to make. But like inter-office memos they can jump from point to point or, on the other hand, dwell at unconscionable length upon a particular point which details the executive’s pet peeve, a point not necessarily germane to the corporate interest, and in that example I think Mozart was dictating just such a memo. He held that series of rather undistinctive and virtually indistinguishable E-flat major themes together with listless scale runs, unpredictable chord changes… like an executive holding forth upon the ramifications of a subject that no one in the front office was much concerned with anyway. ‘Yeah, well, uh, Harry, as I see it it’s got this thing about replacing the water cooler. Let’s just file it and forget it.’ “
More detail, including a fuller transcript of Gould’s rant, appears on the GlennGould.tv web site.
BONUS: Here’s a video in which six other pianists savage and/or worship Glenn Gould’s piano playing: