Way back as a teenager I found an old copy of a James H Schmitz book and was rocked by the great story of Telzey. Then, in the library, a few years later I found the Witches of Karres. I re-read it years later and it held up. Then, yesterday, I found a gorgeous old paperback copy in a secondhand bookstore. Yes!
The sequels to Witches of Karres written my Mercedes Lackey et al are some of the few sequels written by not the original author that work for me.