The Recluce novels tend to follow the same pattern: our hero is different from the surrounding society, leaves home, then discovers something fundamental about the workings of order and/or chaos in the world. They're still fun books to read, but they're fairly predictable.
With The Octagonal Raven, however, there's a mystery to figure out, and there's a complicated conspiracy involved, which makes for lots of possibilities, so it's not predictable at all. The first part was really well done. The second part, which I broke into last night, isn't starting off quite as strongly as the first part (maybe because you actually get some real answers), but the reading I did on the way to work this morning gave me some hope for the remainder of the book.
If you're any kind of Modesitt fan (or if you used to be but got tired of all the chipped crockery in the Recluce books), I would definitely recommend this book. For those who aren't Modesitt fans, I would still recommend this book, but only as long as you're OK with a little didacticism (it's not too bad, really. I think he's done a pretty good job of showing that the issues brought up in the book have many sides).