It's not an especially complex fugue (see, or, rather, hear and read The Art of Fugue) it's the kind of fugue that would impress the kind of person who hadn't listened to or played Bach's famous 48 or his other fugues or had played and listened to fugues by his successors, notably Beethoven, Max Reger, Bartok . . . if I go on that list will fill the page. It can't possibly hold a candle to any of the vocal fugues from any of Bach's cantatas and other great vocal works (hear and see Youtubes and IMSLP scores).
I am certain of one thing, Glenn Gould would never make the claim that it was anything like a rival of those. He was a nut case, he wasn't a pathological, self-aggrandizing, egomaniac. It's what Nicolas Nabokov called "tissue paper music". One of the comments I read claimed that Gould had summed up the entirety of baroque musical practice in the piece which would have to stand as about the stupidest things I've ever read about music if I hadn't gotten responses from Stupy that are in the same stationary race to nowhere.
I have got no problem with people listening to it if they want to, I'd note that this performance, for a CBC radio show - NOT for distribution as a disposable disc by that ad-flyer Simps used to hack for - is the only one I've ever heard of. It hasn't entered into the repertoire. I don't think it's at all as interesting as Gould's musique concrète work, such as The Idea of North. I've written that his career is a tragedy of a composer who was trapped by his easy, too early virtuosity which led to him being a musical spoiled brat and his deep emotional disturbances. I think that effective treatment of that might have freed him to be more than someone who churned out discs that distorted other composers' music to be used as musical wallpaper by the middle to mid-high brow at cocktail parties.
Glenn Gould had some really attractive and even admirable personal traits and even some musical ones, those always were at risk from his tragic mental illness and terrible immaturity which the pampering he received by his public exacerbated. I'd rather concentrate on those whenever I mention him from now on rather than the many unfortunate ones. Maybe I'll just resist the temptation to point out what an idiot Simps is when he brings up Gould the next time. I'd rather not participate in that use of him anymore.
Update: Testing my resolve Simps produces a Youtube of Gould playing the Grieg Sonata in e minor, Op.7 which demonstrates everything I said. The boob posted a Youtube with the score so Gould's distortions are there with the evidence. Just one example, early on there is a ff passage that he plays p which destroys a contrast the ff was obviously meant to be setting up, something I don't think could have been anything but an intentional flouting of the composer's intentions. Then there are the slooooowww tempos, he adds about eight minutes to the time that most of the performers do. And they don't match the written tempos. Believe me, I'm cutting the critique short.
Simps claims to know the piece "backwards and forwards" claiming to have played it. If he understood what it would mean to know it "backwards and forwards" - I doubt he means in the manner of a canon cancrizans, only because I doubt he knows what one is - he'd know that was an absurd claim to make. I doubt he could play the first 3 Hanon exercises backwards and forwards.
I won't post the one he sent but here's Alicia de Larrocha to give you an idea.
It's hardly my favorite piece, though as is often the case with Grieg it's generally better music than it's performances would lead you to believe. De Larrocha plays it as well as I've heard it played. She was a very great artist. It might be the best performance of a piece by Grieg I've heard, though his music isn't one of my enthusiasms. I've never performed him, not even when I played what my teacher told me to. I've never taught him, either. That doesn't mean it's not good music, it just means you can only do so much in one lifetime. If you like it, you're right to go right on liking it.