The first Patricia McKillip book I read was The Forgotten Beasts of Eld. I didn't care for it, and mostly found it dull. I think I considered The Throme of the Erril of Sherrill, but the strange title put me off. Somehow, though, some years later I happened across, as I hope everyone does, The Riddle-Master of Hed. If you haven't read that, drop everything and go get it now.
Despite Riddle-Master's success, not everything McKillip tackled worked so well. The Changeling Sea was preceded by McKillip's only (I think) fling with science fiction (the Moon-Flash stories) - an interesting but uneven duology. It was followed by the Cygnet duology, which started well, but ended weakly. McKillip seems to have been finding her feet before finding the storytelling style she later perfected.
I recall being disappointed by Changeling Sea.I liked it better this time, but it's still not great. It doesn't have the depth of Riddle-Master - not in the story, the characters, the emotions, or the magic. It's a thin volume, and it reads that way. It is charming, in the way of later McKillip books. Peri is a likeable, capable young woman who does the things we might. There's no simpering, no coy smiles, no damsel in distress. Most of the other characters are similarly pleasant.
Changeling Sea should probably just have been a bigger book. There's no room in this limited space to explore everything that's going on, or, better said, McKillip doesn't use the space well. The ending is thin, and tends more toward golden sunsets than the credible, real people that the book is built on. Looking back, it's as if McKillip has found the tone that suits her, but hasn't yet found stories to go with it. Changeling Sea is the start of a good story, but the end of a weak one.
If you're a McKillip fan, go ahead and read. You'll like it well enough. If you're new to McKillip, this is not the place to start. She's an amazing writer, but this book won't prove it. For everyone else - this is light, harmless fun. If you can borrow it or get it cheap, have at it. If not, make it one of the later books you add to your collection, after some of her stronger works.