Don’t let Wikipedia fool you: Diamond is a bonafide academic and Guns*, Germs, Steel is a pretty good read. There’s been plenty of criticism of the work and the author, and much of it holds water, but that’s largely a product of its popularity and influence. You won’t be wasting time if you pick it up, though do take the popular critiques under consideration.
That being said, Charles Mann’s 1491 and 1493 are the best books that cover similar ground while staying rigorous and casually readable. I also wholeheartedly recommend Pekka Hamalainen’s work for a North American lens on the Transatlantic exchange.