The late specfic critic Baird Searles had a great comment some years ago in discussing Sean Connery’s 1981 SF film Outland: there wasn’t a single detail in the film that made him think “Yes, that’s exactly the way the future would be — only I’d never have imagined it!” Which as soon as he said it, made me realize that’s what the film lacked — it’s far-future High Noon riff didn’t offer anything unexpected or surprising. It does offer other good things, such as Sean Connery in the Gary Cooper role, but it’s definitely a weakness (all rights to image with current holder).
Outland is hardly unique in this. Marion Zimmer Bradley’s Thendara House, for example, takes us inside the Free Amazons, the one place for independent women on the violent, patriarchal, psionic world of Darkover. Unfortunately it turns out that the Free Amazons deal with exactly the same problems as a twentieth-century US feminists at the time (should we accept men as allies in the movement?). I found that thuddingly unimaginative (it’s an extreme case of the problems I have with some female leads in historical fantasy).
It’s certainly not a fatal flaw not to offer the audience something they’ve never seen before. Lots of people enjoy series that go over the same ground with minor variations. Why else would I like comic books or Doc Savage, for instance? Even in specfic, there’s no shortage of stories that make no attempt to reinvent the wheel.
Others try to be new and different but are just variations on a theme. A different magic system. A colorful, eccentric detective whose eccentricities are different from all the other colorful eccentric detectives. A cozy mystery set in a different kind of shop from the other shop-owner amateur-detective cozy mysteries. Then again, if you’re a fan of a subgenre, mild differences may be enough. And if the book is really good (great characters, terrific writing, clever plotting, whatever), familiarity may not be an issue. Conversely it’s possible to write a book or movie showing readers something new, but the book still sucks.
Still, if we can write something that’s both groundbreaking and good, that’s a very cool thing. Lovecrafting creating the Cthulhu Mythos. Steampunk when it began (even given there were precursors). Urban fantasy when it started.
I’m not sure I’ve written anything that would qualify, even though I’m pretty proud of my work. But I’m still writing, so who knows?