This is made up almost entirely of eyewitness testimonies. This means they are engrossing to read, as each one is very personal and the tragedy/triumphs are made identifiable to the reader. It also means that the factuality of what is being said is questionable in some cases (usually mentioned in the endnotes).
The book illuminates the vast diversity of experiences during the holocaust. Some avoided ever having to go to ghettos or camps by various means, some escaped from these places and formed partisan units, some joined the Judenrat, etc. Most of the transcripts describe experiences in the east, namely Poland and Ukraine. It seems like experiences in these areas were substantially more brutal than elsewhere on account of the high concentration of death camps, and what appears to be a deep preexisting antisemitism in the local population. In many cases, it seems like the germans didn't even need to instruct the local populations in order for them to lynch jews and expropriate their belongings.
The most satisfying accounts to read were ones of successful revolts, breakouts, or partisan activities. The point of this book is to break the idea that jews were passive subjects of the holocaust. It does a good job.