Ai's journey is long and hard, as it is also for those who wish to help- and destroy him. The book itself is well written, with an intense sense of realism. The people, customs, and biology of the men living on Gethen is well thought out and creates a unique world.
That said, I feel like the core of the story itself lacked something. It did not feel like an action adventure, or a mystery, or a thriller; it felt more as if one was reading historical chronicles (which is what the beginning of the book purports to be.) Many science fiction novels have used this tactic (i.e. Foundation series) but still managed to be exciting; this book did not.