I went to the same grad school as the author did and got a PhD in physics there. Most of the professors I knew who taught the guy said the same thing to me about the book. It's just awful.
So, you mean "awful" like, at some level of Math/Physics the whole thing seems fuzzy and inaccurate or just "awful" even for non Physics Phds.
I can see how it could be seen as pretentious, but not all round awful. He certainly appeals to many lofty ideas which may not be entirely justified by the technical material, but the technical material itself is certainly sound as far as I can tell. The main criticism I would make is that he does not draw a clear enough boundary between accepted mathematical fact and his own speculation.
For me, the thing I like about the book is that it is almost a total mixture of formal logic and poetry. If you don't like it, that is a subjective aesthetic judgement. Same goes for his prose style.
I suppose if you were already fully exposed to all the mathematical concepts in the book when you read it, it would have a lot less value. If on the other hand it is almost your first exposure to these ideas, it's like freebasing pure logic while hanging out in alice's wonderland. Great fun, but I agree not a formal examination of the ideas. It isn't really meant to be as far as I can tell.
You went to the same school as the author(I presume you mean the OP in the reddit thread), and you knew the professors who taught the guy didn't like the book. Is that all you are basing your opinion on?
GEB isn't a physics book, so I don't see how "the professors who taught this guy" say matters - it's all too common that people don't like books that directly relate to their fields; especially so when they deeply vested in their field.
Also, opinion is divided on usefulness of other seminal works as well; to quote a few from comp. sci. - SICP, K&R, TAOCP.