There are some people who don't like Tehanu, but I like it. Tehanu is completely different from the previous Earthsea books, but it's well written and interesting.
I think that Tehanu was written for adult readers and that's why young readers shouldn't read it, because it contains certain philosophical things, which may be a bit difficult to understand.
If you're interested in sword fights and sorcery, this book isn't for you. But if you want to read a story, which has depth, you should read Tehanu.