That top review on Amazon is dumb. Every decent historian knows that history isn't about reciting facts. It's about crafting a narrative given the available facts (as with most things in life).
Given that, this story is still factually accurate on many of its historical components. I researched Japan in the Tokugawa to Meiji period in a pretty decent college (I'll just say it's T20, so not some janky place) and there weren't any major details that conflicted with anything in the story. All the details regarding the Europeans, Nobunaga, Tokugawa, and even that 3-day Shogun is true. The authors made sure to repeat that information on Yasuke was lacking over and over again. But despite that, people still think that the authors "faked a story."
I do want to expand a bit more on this point. When learning about history, such as the Trojan Wars, Biblical history, Pre-Yamato history (basically any history in general), you're bound to encounter myths and exaggerations. Even now as you're reading this, I guarantee you - go on the news right now and try NOT to find a headline that doesn't overexaggerate a real-life event.
So when you read historical accounts, It's best not to treat it as some textbook. Treat is a story that drives purpose into your future.
I think the authors unearthed such a great narrative out of what they were given. And if it weren't for me not buying the book on Amazon, I would have given it 5 stars. Do that for me, will you?