This book has great strengths but one can't ignore its defects.
Still, let's begin with the strengths because the author deserves much credit. As well as giving a good, clear account of the life of Marcus Aurelius he goes out of his way to put that life in context by frequently stopping to explain various features of the economic, social, political and military world within which Marcus Aurelius operated. This is highly welcome. Those long, contextual sections, combined with the analytical chapter at the end, helped to give me a great deal more insight into the Roman Empire than I was expecting. McLynn also does a good job of keeping a complex cast of characters and story moving along without it getting too confusing. I got completely absorbed.
The most significant problem, to my mind, comes with the analysis of Stoicism. Within the body of the book, McLynn is forever tearing a strip off Marcus Aurelius and Epictetus for their inconsistencies and gaps. He knows very well that Aurelius was writing a private journal for his own edification, head-clearing and analysis and that Epictetus did not even 'write' his books since they are basically collections of lecture notes - and, in the case of the Enchiridion, merely extracts from them - made by one of his pupils. Now, if a student of mine wrote down my lecture notes and published them in a book without my having a chance to edit them I'm pretty sure there would be a lot of gaps and probably some inconsistencies. It's not that Epictetus can't be criticised; I can easily do so myself. It's just that on this basis McLynn's criticisms of the extant writings of both Marcus Aurelius and Epictetus seem harsh to put it mildly. It was like reading something by Victor Meldrew when he's had too many cups of coffee.
The same goes for his criticisms of Stoicism in general, both in the main body of the text and in the first appendix. To be honest, I didn't even recognise it as a description of the Stoicism that I am familiar with. For example, McLynn refers to the "Stoic condemnation of pity". My reading of Epictetus, Seneca and Marcus Aurelius suggest not a condemnation of pity but an encouragement to keep it in proportion. All three of those authors, in different ways, encourage generosity, empathy and fellow-feeling. They do suggest that we should interrogate those feelings and be guided above all by our reason with respect to how we follow them up, but that is something quite different. Then there is the claim that Stoicism "subscribes to the dreadful doctrine that if someone suffers misfortune, he himself is responsible". That's just slipshod and misleading. Stoics would say that we are responsible for our REACTIONS to misfortune, which is something quite different. I could go on for several more paragraphs, but I would doubtless bore the reader and certainly bore myself. Suffice to say, if you went by McLynn's account you simply wouldn't have a clue as to why Stoicism has held such appeal to so many people over so many centuries. McLynn says that Stoicism "lacks all nuance" but it is, rather, his analysis that lacks nuance.
I'm also puzzled by McLynn's claim (p.208) that Epictetus died about AD 100. Every single one of my half-dozen sources (books and articles) on Epictetus, some very recent, suggest that he died in about AD 135. Either they are all wrong or McLynn is. If he has some radical new information which suggests that Epictetus died at about the age of 40, information which overturns our previous biographical knowledge, then he should at least have commented on this in the book.
I was also rather disappointed with the chapter looking at the subsequent influence of Marcus Aurelius. Much of it seemed to consist of looking to see if similar ideas are expressed by other thinkers, without necessarily knowing if they have actually read the Meditations. This seems a bizarre methodology. Anyone who has enjoyed grandstanding over a few pints in a pub knows that it is quite common to come up with philosophical ideas that remind your companions of other thinkers that you've never heard of. Also, I frequently engaged in pantheistic reveries as a teenager, before I was even aware of philosophy, let alone Marcus Aurelius. I won't share these thoughts with you here; again, I don't think our boredom thresholds could stand it.
Let's finish on a good note. Due to the depth of McLynn's work I came away enriched. I had a deeper much more sophisticted view of both Marcus Aurelius and the Roman Empire. Indeed, my thinking about both has changed significantly and is now much more mixed - dare I say 'nuanced' - than it was. I wasn't expecting quite that level of impact. So, for that reason alone, and notwithstanding the above points, I'd still recommend this book if you want to understand the man and his time.