I bought a copy of Worldbinder in the states, and although it is a cracking book, I now have a prolonged wait for the next (final?) instalment.
Simply put, Worldbinder takes takes Farland's series in a new and pleasing direction. At the end of Sons of the Oak, Fallion and co. were slowly gaining the upper hand, defeating the evil Shadoath and growing in their new powers, free from the morally suspect reliance on forcibles and endowments.
Worldbinder tips everything on its head, and makes the situation far worse for our heroes. A major character dies and even more of humanity perishes as the threat intensifies - it would be unfair to give away too many details, but I was particularly pleased that Farland is tidying up seemingly loose ends.
I was always frustrated by the unfinished quest to find Daylan Hammer in the original saga - it seemed forgotten, abandoned in the rush to complete Lair of Bones. Now we learn why the quest was unsuccessful, and the true location and identity of the mysterious Hammer. We also learn the identity of the Bright One owl that also appeared overlooked in the past.
2 criticisms of the book prevent four stars - first, it is unrelentingly bleak, and second some of the sequences (humanity besieged by a huge ravening horde, again) seem a reprise of earlier battles with the reavers.
So, no 5 stars, but a good lead in to (hopefully) the final part of an original premise.