Clearly a lot of work has gone into this book. Unfortunately it still would have benefited from more professional editing. The references are a bit of a mess, there are noticeable typos, key concepts are not explained as well as they could be, and for key moments (like the night of the accident), the book is overly reliant on other published works. But if you know you are reading an amateur production these things are possible to get past. While a reader would probably benefit from having existing familiarity with the disaster and its causes, it still provides some useful detail to someone coming in fresh.
Another quibble is that despite wanting to put down an objective account, it’s intrusive how much he clearly supports nuclear power.
The travel narrative is by the author’s own admission less interesting than the main narrative, and we don’t really get a sense of the personalities of many participants (other than Dyatlov being impatient), or even the author himself (other than someone who enjoys video games, photography, and exploring abandoned places). I read it on a Kindle app on iPhone, which probably doesn’t do justice to the photographs. My thought on how to deal with contentious topics like casualty figures, in a case where you are not a specialist yourself, would be to interview some experts to have them give their perspective on things.
All in all, while I am impressed by what is clearly a labour of love from someone who is very passionate about the subject, I would guess that there are better published works about Chernobyl out there.