In writing a blurb (or a query letter), it's crucial to find the true core of your book. If you shoehorn your book as a high-octane adventure, that might draw in a different readership, but they're going to be disappointed pretty quickly. If your book's strength is complexity, maturity, philosophy, then those are what your blurb should be showcasing.
Here's the back copy from a recent favorite, Ada Palmer's Too Like The Lightning:
Mycroft Canner is a convict. For his crimes he is required, as is the custom of the 25th century, to wander the world being as useful as he can to all he meets. Carlyle Foster is a sensayer--a spiritual counselor in a world that has outlawed the public practice of religion, but which also knows that the inner lives of humans cannot be wished away.
The world into which Mycroft and Carlyle have been born is as strange to our 21st-century eyes as ours would be to a native of the 1500s. It is a hard-won utopia built on technologically-generated abundance, and also on complex and mandatory systems of labelling all public writing and speech. What seem to us normal gender distinctions are now distinctly taboo in most social situations. And most of the world's population is affiliated with globe-girdling clans of the like-minded, whose endless economic and cultural competion is carefully managed by central planners of inestimable subtlety. To us it seems like a mad combination of heaven and hell. To them, it seems like normal life.
And in this world, Mycroft and Carlyle have stumbled on the wild card that may destablize the system: the boy Bridger, who can effortlessly make his wishes come true. Who can, it would seem, bring inanimate objects to life...
Being immersed in ideas and "a mad combination of heaven and hell" is the hook, and to plenty of readers, it's a much more enticing one than "WILL OUR PROTAGONISTS SURVIVE".
Or, here's the blurb for Nina Allan's The Rift, which has almost no plot at all:
Selena and Julie are sisters. As children they were closest companions, but as they grow towards maturity, a rift develops between them.
There are greater rifts, however. Julie goes missing at the age of seventeen. It will be twenty years before Selena sees her again. When Julie reappears, she tells Selena an incredible story about how she has spent time on another planet. Selena has an impossible choice to make: does she dismiss her sister as a damaged person, the victim of delusions, or believe her, and risk her own sanity in the process? Is Julie really who she says she is, and if she isn’t, what does she have to gain by claiming her sister’s identity?
This one pounds hard on the book's theme and underlying tensions. Which is great, because that's where the book's heart is. Note, particularly, how this isn't even framed as an investigation of "what happened to Julie"; the book's heart is in Selena's response to Julie's return, and so that's what the blurb focuses on.
Do note, however, that both of these books have some very vivid elements mentioned in their blurbs. Too Like The Lightning has outlawed publicizing religion and gender. The Rift has Julie's mysterious disappearance and return. These aren't all either book is about -- but those are good, eye-catching details to hang a story around.
Your story probably has its own central elements, too. The things that make it special; the things that make it interesting. That's what you want to be emphasizing in your blurb -- in a way that sounds enticing. As long as it excites you, you can probably articulate why -- and that's precisely what your blurb should have.