I perhaps came to this book a roundabout way, having read The Book of the New Sun twice, The Book of The Long Sun a time and a half, and The Book of the Short Sun once. I'll keep this spoiler free for the entire solar cycle.

The Book of the Sun was written as a singular text and split into volumes at the behest of the editor and publisher. It was well received and earned him a reputation as one of genre fiction's more literary authors, if not the very peak. Wolfe has a way of not explaining plot points fully, leaving mysteries for the reader to intuit or infer, sometimes right before abruptly shifting to the next scene. Occasionally, he will pepper the next scenes and chapters with an offhand remark or clue that will make everything click. It's rarely too much, just enough breadcrumbs to give the reader an epiphany about confusing events or completely reorient their interpretation of power dynamics between characters. Enough to realize that he's trusting you as a reader and you should trust him as an author. Figuring out what's going on is a reward in itself. Putting in the mental exertion and getting the endorphins from that epiphanic payoff is a large reason why his books are so enjoyed.

The Book of the New Sun is obtuse though. There are some events that leave the reader still scratching their head after multiple re-reads. It was confounding enough for the publishers to push for another book to spoonfeed some of the answers, and so The Urth of the New Sun made it to print. It's a coda that stands outside the text of the Book of the New Sun but informs it and is nevertheless "canonical." However, while enjoyable and adding some mysteries of its own, it lacks the charm of its predecessor. The prose isn't as beautiful and there are times things are explained too much.

Structurally, it reminds me Grimmelshausen's Simplicius Simplicissimus, an early German picaresque novel set in the 30 Years War. Divided into five books, the first four involve a German youth, Simplicius, going out to the world, having misadventures, and ending up in France before heading back and encountering the same people again but with different perspectives. Like Simplicius, The Book of the New Sun's protagonist Severian goes through his world in four books gaining perspectives, and repeatedly encountering the same people along the way before returning. The fifth section of Simplicius Simplicissimus is often seen as an unrelated fantasy adventure, but I think it recapitulates the first four on a metaphorical and spiritual level. Likewise, Urth of the New Sun in its own way a spiritual journey that recapitulates (or at least revisits the locales) of the preceding books.

Grimmelshausen went on to publish a sixth section of Simplicius Simplicissimus after the success of the first five books, and Wolfe borrowed the name "Baldanders" for his series from that, so he was at least familiar with the work. Overall, I feel like Urth is the weakest of all Wolfe's solar cycle books, but who knows, maybe my opinion will change with a future reread and reevaluation.