I had been looking forward to this one, famed as one of the best Doctor Who novelisations, and I was not disappointed. Cotton has recast the narrative of Dennis Spooner's TV script into epistolary/diary form: letters from Ian Chesterton to his headmaster, the Doctor's own diary, letters from Ascalis the assassin and Locusta the poisoner, and contributions also from Barbara, the Emperor Nero, and Nero's wife Poppæa (but not Vicki); the whole thing framed in a covering note by Tacitus (obviously written several decades later). Eye of Heaven, the best of the spinoff novels featuring Leela, also featured multiple first-person viewpoints, and I've read first-person narratives in other First Doctor stories (here, here, and partly here), but this is the only case of the whole thing being ostensibly done from written records (the Doctor having compiled everything and then left it behind in the villa for the archivists to discover).
Admittedly, as an actual story it's no great shakes, and purists will be disappointed that we lose a lot of the funny lines from the TV version and one of its major comic elements (the two pairs of time travellers not actually meeting each other in their wanderings). But the whole thing is done for language and laughs; it's meant to be fun, and it is fun, and that's all you can really ask.