The history is an easy read, assuming that a four year long human catastrophe can be called easy. Optimistically, the war could be called an organized generational genocide, but pessimists would sure use harsher language.
The history is a survey work, delving into details where needed, but mostly focusing on the big arcs and the worldwide theatre. Like all war histories, it's rife with names and locations, enough to leave you dizzy and desperate for an atlas. Marshall generally does a excellent job in taking all those dizzying fact and creating although sometimes overly details narrative.
One place where the narrative bogs down is in the description of the armies. If you aren't into the military aspects of history, the movements of Division III and Corps V will make your eyes glaze over. It's just too much to take in at times, often obscuring the narrative of the battle rather than informing it. It's here that Marshall shows military dinkage, where mastery of details overwhelms situational understanding.
With all the military minutia, if I hadn't been learning about modern army organization recently, I would have been completely lost.
The history itself won't stand against any more detailed history, nor any narrower one, but that's no nock against it. From the beginning, the work understands the limits of its narrative, consistently knowing when too far is too far, even with its military dinkage. The history keeps its eye broad, surveying events in France, Russia, the Middle East, Messopotamia, and the Balkans.
For the student of general history and other eras, it serves as a firm refresher of those four dreadful years. For a student of WW1 history, I doubt that this book has anything additional to offer, even as a refresher.