Leviathan Wakes would not be nearly as good if the exact nature of what comes later was broadcast early on, though the prologue does make it quite clear that the central mystery is going to lead somewhere outside of established science fact. That’s the promise it makes: that there’s something strange going on, and that by the end of the book you’re going to know more about it, and about what happened to the point-of-view character.
IMO, straying out of the lane of the subgenre that someone going in with no foreknowledge happened to sort a story into without reading the whole thing first is pretty low on the big list of literary sins. On the contrary, I think a genre switch-up executed well is a delightful thing, mostly because complications and reversals are critical elements of most good plots and genre is completely arbitrary and artificial. All other things being equal, a story that tiptoes around genre conventions is never going to be more interesting than one that goes where it wants.
IMO, straying out of the lane of the subgenre that someone going in with no foreknowledge happened to sort a story into without reading the whole thing first is pretty low on the big list of literary sins. On the contrary, I think a genre switch-up executed well is a delightful thing, mostly because complications and reversals are critical elements of most good plots and genre is completely arbitrary and artificial. All other things being equal, a story that tiptoes around genre conventions is never going to be more interesting than one that goes where it wants.