Trajan was in Roman eyes one of the greatest emperors, and his achievements both domestic and foreign were remarkable, and yet because we have so few real sources close to his life, there's a real lack of modern writing about him - he's just not an attractive project for a biographer. I'm aware of one other modern book that looks at him properly, though I haven't read that yet. So I was pleased to read this.
But it is an odd book, though you don't realise its some of its oddness until you are done. Firstly, there is the inevitable reality that so much of Trajan's life is simple guesswork - that's fine for the first chapter, where the author fills out family background and guesses what kind of schooling Trajan had and so on, since it's so clearly guesswork. By the time you get towards the end and we're hearing just how lovely and friendly his home life was, it gets a bit wearing, as this frankly is just taking Trajan's own propaganda and running with it. There's a lot of guesswork in this book.
That makes it stranger still that Jackson never really discusses his sources or their reliability. Where is he getting his information? There are a few brief mentions of a historian or two, and a lot on Pliny's panegyric, delivered when he became consul, but very little on how we know what we know. And of course there is some on Pliny's famous letters, but less than you would expect. Occasionally comments betray a lack of familiarity with the sources - he thinks that Arrian's description of Trajan as 'king' ('basileus') is an error, when it's actually a perfectly regular Greek term for a Roman emperor.
In the end this is mostly narrative history, and so it doesn't mine Pliny's letters, for instance, as deeply as one would like on the changing administration of the empire.
Interestingly Jackson is an amateur historian, with a day job in something quite different. It's impressive, considering that fact...but it doesn't live up to the rigour of an academic history, and so falls short of what I'd hoped.