Some critics think reader expectations are a sign of moral/intellectual failing in readers, and thus frustrating reader expectations is a moral imperative for "serious" writers. They rail against readers who insist they know what they want, and writers who give it to them.
I don't agree. I feel that there's an implied contract between reader and writer...like that between dance partners, where the leader signals to the follower what's coming next, so that neither trips up nor gets stepped on. The writer can write whatever he/she pleases...but owes it to potential readers to state the kind of dance they're going to be doing, and not change from (say) a waltz to a jitterbug in mid-dance.
Example: as a child I loved horse stories. The horse stories I'd been reading were written for children, and though sometimes horses died (in Stormy, Misty's Foal, for instance) and sometimes parents and kids differed about whether the kid could have a horse, the general tone was positive: the child protagonist came out of the story feeling OK. Then one day the librarian handed me John Steinbeck's The Red Pony, which some purblind cataloguer had told libraries should be shelved in the children's section (I saw the card later--a boy and his pony, it said.) The Red Pony is the story of a boy in a dysfunctional family whose pony dies--gruesomely--of strangles. It is NOT a child's story...it just happens to have a juvenile POV character and a horse in it. That story violated the child-horse-story contract. I did not become a better person by reading it, nor did it improve my grasp of literature.
Giving the reader the kind of story they expect does not mean writing a dull, boring, predictable story. It does mean respecting a reader's choice: that if they bought a romance, they want a romance in it, and if they bought a whodunnit, they want the criminal exposed. It's OK for them to want that. It's OK for you the writer to give it to them. You can play with the conventions of genre, if you want--you can add decorations, change the color scheme, twist the plot into curlicues--but readers deserve the courtesy of getting what they asked for.
Part of the art of storytelling is surprising the reader in a good way...giving them a flavor, a tone, that does not negate, but enhances, what they like about their favorite kind of book. You have a lot of scope for that, in any genre, without frustrating/angering the reader by breaking faith with him/her.