A. S. Byatt was a brilliant writer, all too often forgotten these days because her style of writing - big, deeply intellectual books that don't set out to charm the reader with easy levity or irony - is not fashionable. I adore Possession, a book I absolutely ate up as a teenager.
I also recommend Angels & Insects, a rather weird and perverse set of novellas, and from her Frederica quartet (which I haven't completed) I had a ball with Babel Tower and its quite grotesque pastiche. Recently I read her introduction to Iris Murdoch's The Bell and it was *stonkingly* good.
She taught my seminars on T.S. Eliot (and we had chats about forgotten genius Dorothy Richardson) while I was at University. She was known as Mrs Duffy & some the male lecturers were underhandedly beastly to her (envious gits) Her sister Margaret Drabble used to come in to give one off talks too.