This was the first book of Ursula that I've read, even if I'm used to read Scifi from Asimov, Clark and Heinlein. But Ursula is a complete different style from those.
"Changing Planes" can be described as "she took her dreams and turned into stories". It's a story of several "planes" of existence, each with its own history, its own culture and its own people. Each is different from the other in almost non-overlapping fashion.
At first it's kinda weird and uninteresting -- till you realize how much creativity one has to have to come up with several different different planets and their history.