Science Fiction

One of my favorite themes is social commentary in science fiction. The Expanse is a great example: humanity colonizes the solar system, but instead of achieving some kind of utopia, it just becomes a continuation of the same class warfare that has always existed on earth. Even when the alien tech opens up essentially unlimited free real estate, some corporation still gets into a violent conflict with the belters over a lithium mine.

Strong world building. No matter how farfetched the technology/society/species, if there is enough backstory or precedent anything is believeable. For example, Isaac Asimov's robots aren't realistic at all but he starts by laying down a set of rules (three laws of robotics)and wrote entire books worth of stories detailing their development. This not only allows readers to suspend their disbelief and accept that sentient robots exist but gives context and relatability to all of your characters/events/locations. The Expanse acheived the same by simply rooting it's fiction deeply in reality which makes it inherently relatable. The rest is normal storytelling.

If you liked the Expanse you might be interested in Kim Stanley Robinson's Mars series, and for the same reasons.

As for your original question, for me the important part is good writing and story telling. Some writers' styles just turn me off no matter how good or important the work is. Narrative style is what makes or breaks a book for me no matter the genre.