And over half a dozen historians at my university spoke highly of the book when I discussed it with them. I'm going to put the opinions of history professors above anonymous posters on the internet. Many mainstream historians are shifting away from the "great man" style of history that puts emphasis on culture and actions of individuals, and towards a more geographic lens of history.
The bulk of the criticism I've encountered (besides attempts to equate it with racist environmental determinism akin to Herodotus) are that it gave insufficient attention to advancements in human knowledge and understanding that changed the landscape of advantageous and disadvantageous geography. This doesn't hold much water, from what I could see in the book. In fact, one of the central points of the book is that access to the New World (which was brought by advances in maritime navigation) drastically altered the course of Western European history. Prior to that, South and East Asia were broadly speaking more developed than European societies with greater population density and larger urban centers.
If you actually read through the responses in the search I linked, you'll notice that the discussion is a little more nuanced than "it's perfect" or "it's trash". It's certainly not perfect in terms of analysis of historical evidence—there are far too few primary sources to support his claims directly, and the trends he points out can be picked apart in particular—but it still has compelling evidence that would be considered valid in other disciplines. I suspect your own professors had a more nuanced opinion than simply "spoke highly of". That doesn't sound like an academic to me.
Additionally, you should check the subreddit out. It's very aggressively moderated and many of the posters are openly credentialed professors or are actively doing graduate research. I have found it's also a great place to keep your eyes open for preprints.
I did read through the responses. The highest upvoted comment on the post "What do you think of Guns, Germs and Steel?" comes from someone that explicitly says that they are not a historian. The bulk of the criticism comes in the form of people alleging environmental determinism and the denial of human agency, which isn't actually a criticism of the book but rather a rejection of book's core claim that geography is a more decisive factor in human development than society and culture. That, and a healthy helping of people alleging western chauvinism, despite Diamond explicitly rejecting the narratives of Western social or racial superiority and pointing out that Western Europe made little contributions to Eurasian development until the mid-late 2nd millennium AD.
Sure, my conversations with professors were more nuanced: one talked about how the geographic analysis prompted them to examine history through the lens of quantifying available resources to a society and levels of urbanization. They agreed with the core theses of the book, and said that it offered good refutations to the common layman's narrative of Western cultural superiority. I could spend the rest of my evening recounting the conversations in the comments here but for the purposes of this discussion saying that they "spoke highly of" the book conveys what is necessary.
The bulk of the criticism I've encountered (besides attempts to equate it with racist environmental determinism akin to Herodotus) are that it gave insufficient attention to advancements in human knowledge and understanding that changed the landscape of advantageous and disadvantageous geography. This doesn't hold much water, from what I could see in the book. In fact, one of the central points of the book is that access to the New World (which was brought by advances in maritime navigation) drastically altered the course of Western European history. Prior to that, South and East Asia were broadly speaking more developed than European societies with greater population density and larger urban centers.