As almost every other reviewer has noted, this book is not a history of the Korean War, despite the title. It's more of a collection of historical essays on the Korean War, focusing largely on atrocities committed by US and ROK forces on South Korean civilians and the lack of balance in what little there is written about the war. Cumings is not shy about his political sympathies, which will turn off many readers.
That said, every horrifying event presented in the book is backed up by thorough research from unimpeachable sources, including declassified US and ROK documents as well as the findings of the South Korean Truth and Reconciliation Commission.
This would be a five-star if the title were more honest and the writer were a little less strident. I'm afraid the general tone of the book is going to alienate the people who need to read it the most.