The loneliness of the long distance space traveller. I love the turn of phrase in the writing, the adorable little vignettes, and the sense of personality of the protagonist, lost in space and going slightly crazy. Really feels like it sits in the tradition of French science-fantasy: I can imagine a Moebius comic strip telling this tale.
It even has a central plot, with an interesting and satisfying conclusion, going for it too. But far too few people will actually get to see that plot, as the game is ridiculously hard. Impossibly hard. I ended up playing a modified version just to see the story.