Sometimes a book comes along that completely knocks you off your feet. A perfect example is A Fire Upon the Deep, by Vernor Vinge. It takes all the tropes of space opera, but grounds them in interesting speculations about physics. It is a war story, but told from the viewpoint of refugees fleeing that conflict. It is a heroic quest, but set in a far future society that travels between stars. It pushes all the emotional buttons, and keeps you on the edge of your seat right up to the last page.