I'd heard a great deal about the Book of the New Sun before finally deciding to pick it up. I knew the general outline of the premise, and I was familiar with much of the praise directed at the series, so I know that in theory one reading is not enough to fully appreciate what's going on. I also have the distinct impression that I will need to read Sword & Citadel before really having a complete picture of the thing. 
 That said - Gene Wolfe does some amazing worldbuilding in this. The descriptive writing, the approach to unfamiliar terminology and concepts, the setting itself, all of them are engrossing and engaging, and frankly they were the highlight of this book during my first read. Some of his narrative techniques are also quite effective - the way he uses callbacks and foreshadowing, the elisions and the retreading of familiar events, the narrator's position in space and time, and so on. The structure of the story is quite interesting in and of itself. 
 The plot of the story itself meanders in fits and starts, though - the protagonist Severian almost seems to bumble into plot points, and a great many things are driven by the force of sheer coincidence, or so it at least appears. The first volume here, Shadow of the Torturer, barely feels like a complete story (and even the whole of Sword & Citadel mostly feels like an opening act or two), so this is something you'll need to be in for the long haul. 
 Severian himself, our protagonist and narrator, is unpleasant in several ways, and I'm having a hard time deciding whether this is to the detriment of the reading experience or not. I certainly don't mind unlikable protagonists, but there's something about Severian's sometimes casual cruelty, his impromptu ramblings about the nature of love and lust and women, and his unstable yet apparently very strong political allegiances that are disagreeable in a way that is off-putting to the narrative itself. 
 And speaking of women, don't come here looking for balanced or mutually satisfying relationships. Seemingly every woman Severian sleeps with is in a position of powerlessness when he does so, women who try to fight for themselves generally end up being punished by the plot, and there's a sense that the narrator, at least, sees women as properly inhabiting a narrower field of opportunity (whether the story ultimately supports the narrator's views on this is less clear). It was jarring to read, though since this was written over thirty years ago I did go into this assuming there would be at least some gender baggage like this. 
 Overall, despite its irritations, there's a core of something really enthralling in this first half of the Book of the New Sun, and the world and atmosphere it explores. I can see why it's inspired so much love, and I'm certainly interested in reading the rest of the series, though I'll be steeling myself against the ways in which it's painfully out of date.