I think that the best book I read this year, in terms of entertainment, was Across the Nightingale Floor and its sequels. It was a fun adventure set is a mythical Japan, with ninjas and samurai and bloody battles galore. I've only read the main trilogy; there's a prequel to the main series and a fifth volume that wraps things up neatly.
If I'm thinking of the book I thought had the most literary merit, I think I would go with When the Emperor was Divine. It's written with a lyrical, dreamy style that brings the WWII Japanese internment camps to life while preserving the anonymity of individuals. It's beautifully written, and haunting.
What about you guys?