This kind of word is an eponymous adjective. Wikipedia has a pretty comprehensive list of English eponymous adjectives. (The list includes many eponyms who are not writers, but as most persons worthy of distinction by such an adjective expressed their influence through writing, most on the list are authors of a kind.)
This list includes Shavian as relating to Shaw's works or style.
However, these adjectives are coined as necessary, and though Hemingwayesque and Twainian - mentioned in a comment - are rare enough not to show up in this list (nor yet in Google Books, as indicated by an Ngram), they are equally valid terms.
Virtually all eponymous adjectives simply add the -ian/-an suffix to the eponym, though -esque, -ic, and -ine also show up (to my ear, those respective suffixes are used indistinguishably in this role). If you're making one up, and you can't find a precedent, either -esque or -ian should be readily understood.