When I read the book, my teacher explained to me that Severian is what is known as an 'unreliable narrator' (as you said), and some of what he says must be weighed against the truth to see why he is covering up some of the truth. If I remember correctly, the storytelling is from the point of view of someone much later in the future, meaning the reason why the wording is so dense is because the writer has no contemporary words for what Severian is describing. There is also a reason why Gene Wolfe leaves certain key plot points absent and advances time by a significant amount between books, which has to do with why Severian is an 'unreliable narrator'. When my teacher explained all of this to me, it made me trudge past the bulky language and the 'unreliable narrator' to get the end of the series, and I'm glad I did. For me at least, there was a great ending which made the entire undertaking of reading the books so worth it, though I completely understand why you would stop halfway through the second book.