This book is a good account of the times of Constantine XI Palaiologos, the last Roman Emperor (r. 1448-1453) and his misfortunes (despite his competence and bravery). It explains well the events around him, but I must warn that the details on the siege of Constantinople are relatively succint. That's acceptable bacause this isn't a book on the siege of Constantinople. It also gives a very good light on the transformations of his image after his death and the use of profecies around him to bolster the Megali Idea and the Russian ideology of "The Third Rome".
Despite Nicol's clear competence (by the way his style of writing is very readable), I have 4 small issues.
The first of them is that I don't think the man behind the office wasn't represented enough (especially on the first chapters), even if that's a very tough task considering the relative scarcity of materials regarding the imperial private life (if there was one) and the fact an Emperor was almost always represented in a stylized way. That's the case of his surviving seals where it's more the office and not so much the person is being depicted, as the imperial crown appears on the top of Constantine's head (he was never crowned). This is important because Nicol's work is supposedly partly a biography. At least that attempt wasn't completely unsucessful.
The second one is his romantic assertion on page 89: "[..] On the whole it is perhaps best to accept one or other version of what the last Byzantine historians have to say about Constantine's death. It is certainly kinder on the memory of one who was without a doubt a courageous man of action, 'a prince worthy of immortality', as Sagundino called him." Although he backs very well his opinion that Constantine XI was at least killed and probably beheaded, it gives the idea he's being backed by very strong emotions. A historian should try to abstain from that as much as he can.
Besides that his last chapter, even if it's interesting to know about the fate of the Palaiologoi (namely those who went to England) and all its associated impostors, was a bit out of the subject of the title.
Finally, I felt much of his material on Constantine's life and the setting he lived in (especially on the former chapter) was reused material from his other book The Last Centuries of Byzantium, 1261-1453, which was constantly referred to on the footnotes. I hate when this happens.
Even if it has its flaws, this book is recommended for all those who want to learn more about Constantine XI.
P.S.- The pun the author made with Constantine, The Last Emperor Of The Greeks (the only other monograph on the Emperor in English, published in 1892 by Chedomil Mijatovich) is fun.