Heliopause looks, on the surface, like far-future SF. It's a veneer. A very good, lovingly crafted veneer, rich with knowledge of astronomy and the knowing evocation of tasty SF tropes; but the heart of the game is fantasy, and this is understood, and it's very adeptly handled.
The framing of the story makes it clear that we're dealing with a tall tale, a reliable signal not just of narrative unreliability, but of entry into realms of Story where versimilitude is beside the point. The threefold repetition, the fisherman's-wife motif of a fourth greedy wish cancelling the previous three, the three gifts whose use emerges only at the moment of crisis -- these are solid motifs of the fantastic, and deftly employed. The protagonist gives lip-service to the idea that he's collecting stuff for its unique scientific properties, but really what's being sought isn't something with a technical application so much as Herodotean wonders.
SF treats space as a rational quantity to be managed in some way or another: an ocean to chart, a frontier to advance, an empire to administrate. In Heliopause, space is the Great Forest of Arthurian knight-errant and Grimm fairytale, or the ocean of the Odyssey: anything might be encountered there, but you won't be able to plot it on a map. The principal controls, which you're given enough time to figure out intuitively but not enough to really master, feed into this feeling, as does the low-level approach to scenery; the standard IF game encourages a rather Aristotelean, sift-through-lists approach to one's surroundings, but this feels more like fable than fieldwork. The problem with this in a game context is that things end up feeling quite linear; the sense of vast possibility in the early stages gets closed down towards the end.