As a first thing don't be put off by the book's small size. The paucity of contemporary sources on Belisarius doesn't allow for hefty tomes if the writer's purpose is history and not speculation. And Hughes' purpose is to make the facts clean about Belisarius' military record and assess his worth as a commander.
The book is well furnished with drawings and maps to allow the reader a quick grasp of the situation.
The chapters are kept well short, allowing the reader to focus on the single events yet never lose sight of the broader picture.
Hughes also introduces up-to-date knowledge, especially when describing the "Roman" army, its enemies and their weapons and equipment.
Differently from other authors, Hughes always keeps an impartial posture: he doesn't set out to demolish Belisarius or exalt his deeds. I won't spoil what his conclusions are.
However there are two problems with this book.
The first is in some chapters, especially those dealing on the relationship between Belisarius and his wife Antonina, Hughes' style becomes convoluted and much harder to follow. It's obvious Hughes would have preferred to do away with analyzing this relationship but, as Antonina's machinations often affected Belisarius' military and public career, he had to do it.
The second is there are some errors in the text which obviously made it past the editing process. The blame here lies probably more with the publisher than with Hughes.
All in all this is an excellent book, highly recommended to all of those even remotely interested in the history of Byzantium.