I read the trilogy which I enjoyed a lot and then squeeed when I found an unknown sequel (the Harsh Cry of the Heron) in the library this weekend. I finished it yesterday morning and thought it excellent (and spent the last half hour in tears, but thats another matter!)
I would definitely start at the beginning- Across the Nightingale Floor. I think I have the second one if you'd like to borrow it.
Its been a long while since I've read such an impressive and beautiful world with such real and diverse characters, some of the imagery is fantastic.
Anyway, I think you've gathered that I thought it was good!