I quite like the book and it's structure; part I regarding elements that influence battles, and part II example narratives of battles and what happened at them, with a thematic summary of each.
You can pick it up read a little and then leave it for a day or so quite easily.
I've spotted one mistake, whilst discussing the Hydaspes in 326 BCE, between the Alexandrian Macedonians and Porus' Indians Montagu mentions casualties "On the Roman side" and again "losses among the Roman infantry". A glaringly bad error. Still the book is quite good for the general reader.