There are other books in Slavic climate but Witcher -though not straightly Slavonic but based on Slavicism is indeed a world class literature. Sadly only Polish readers are able to fully enjoy the master word craftmanship of Sapkowski because many things is untranslatable. And don't read in English ,maybe there is your native version of Wiedźmin because this Saga have its years and was translated mostly to Slavonic languages.
btw. Sapkowski as a person is an horrible asshole!