Characters that can keep me guessing. Severus Snape in the Harry Potter series is a great example of this.
Dialogue that flows…
One liners that can make me think, make me laugh or ideally do both.
A story or novel I don’t want to put down and it takes the need for sleep to do so! That’s what I call a good tale.
Phrases that “hit the spot” in terms of aptness for the character, the situation and so on. Wodehouse’s flowery prose (by today’s standards) is so appropriate for Bertie Wooster but would be hopeless for a more modern character.
Stories that can make me “feel”.
I learned a long time ago if someone makes something look easy, that said someone has worked their socks or other hosiery items of choice off for years to get that effect. So when I read “easy to read” prose I inwardly salute the author who’s inevitably spent years on improving their writing.
I love series novels and Terry Pratchett has several within the Discworld series - Vimes, Death, Witches, Wizards and so on. I love seeing the characters develop over several novels as well as in each individual one.
Well thought out plots. Twists that genuinely surprise. (I don’t mind spotting some in advance of the denouement but if I get to guess them all it spoils the surprise).
I adore well written, well rounded, gusty heroines. This is why I much prefer to the lively Elizabeth Bennett to the, my mind, duller Fanny Price (Elizabeth gets into predicaments of her own making and works to put things right. Fanny gets her man mainly because bad things happen to others to bring him to her - or at least that’s how I’ve always read Mansfield Park).
Stories that challenge injustices (To Kill a Mockingbird and most of Dickens’ back catalogue are good examples!).
Stories that change my mind about something I thought I knew. The Daughter of Time by Josephine Tey changed my opinion about Richard III.
Stories that take me completely into their world so when I finish reading I feel almost bereft, sorry to go.
Stories that show me a whole new world. Sci-fi and fantasy are the best for this. Yes I know I can be shown a whole new world on earth but I prefer what other worlds in some universe could be like.