I read The Summer Tree and underwhelmed, so I never finished the series. It had all the things I hate about bad alternate worlds stories: a bunch of incompetent people from our world go to another world, Have Epiphanies, and Fix Things that the inhabitants of the world are incapable of fixing, even though our heroes are completely ignorant of the new world and how it functions.

But I've heard such good things about his later books that I may try him again. Tigana seems to especially well regarded.