Well, actually I finished it like two days ago. It was pretty good. Incredibly dense, though. It helped once I realized that all the philosophy (in the second book, the main character spends a lot of time trying to figure out...something, regarding the nature of feeling and emotions) was intentionally a bit muddled and contradictory.
However, there is something interesting there. The whole book is about the main character's vague intuition that this world isn't enough. Ulrich doesn't know himself and doesn't see himself as possessing any essential qualities.
There's a constant temptation, in the book, for him to veer into the mystical and ecstatic, but he keeps pulling himself back: somehow Ulrich, a mathematician, can't abandon a certain scientific, rationalist mindset. He keeps trying to somehow rationalize the scientific and mystical viewpoints--eventually he begins circling around the idea (initially a joke) of subjecting feelings to scientific analysis. The first book is a sort of satire of a world that has no center: an entire empire that is desperately looking for something to believe in.
The second book is the beginning of an attempt to provide answers. Unfortunately, it doesn't really get anywhere. But there is some interesting stuff in there. Ulrich starts by breaking down the simple dichotomies that had (even then) begun to dominate psychology: man is not simply a creature who seeks pleasure and avoids pain--there is much more to our emotional life than pleasure and pain. There are these tremendous and strange movements in our emotions, and we barely understand what causes them or how to describe them. And life lies somewhere wherein these movements.
For a time, Ulrich thinks it might be possible to achieve a kind of mystical communion with his sister, Agathe, but this feeling wanes without them quite knowing why. Perhaps its simply because other people--no matter how perfectly suited they are to you--can never be the answer. This is not one of those unfinished novels (like The Trial) that feels complete. There is something very unresolved here. Actually, it's not clear that it can be resolved. How would a novel like this end? With Ulrich finding the secret to life?
It was an interesting book. However, I'd have to say that out of all the books I've read, it's probably one of the ones that I understood the least (much less than I understood Paradise Lost or Ulysses). To the extent that the book was a story, it was breezy and enjoyable. But to the extent that it's a work of philosophy, it was pretty slow going.