For me this story had a wonderful collection of pieces that somehow never came together properly. The scene was open to many possibilities. The loss of self, isolation, cabin fever, loneliness and state of mind was definitely thought provoking. The sex/rape, particularly as the definition of the relationship but never having communication was both clever and posed a question. The writing was artfully done, allowing the impact of the scene through clever language instead of blunt words.
... Yet they never all came together.
I agree with those who felt the scene was too static. The endless sameness of it was something that either needed to be better built upon by other aspects, or just cut down to one scene. As a flash piece this could have been done very nicely. But the lack of development over time of the character never shone through, the result was the piece felt like one scene, not a real story.
Which leads into the portrayal of state of mind. The scenario was one that could have gone many ways, insanity, communication, acceptance, introspection to name some off hand. Early on I was curious to see where the character went, what does she turn into or discover when left only with herself and an alien she cannot really communicate with? Ultimately this fell very flat for me in delivery, the questions were never really posed significantly and the story seemed to be that she survived and chose to keep doing so. This was perhaps where the story most fell apart for me, no real "story", just a moment (albeit a very long one) of existing and not dying.[1]
The sex/rape I thought was quite well done in how it was presented. The interaction was simply all they could do and the lack of communication kept it from being erotic (although I am sure some people found it so). I think it added to the horror, closeness and isolation of the character, but occasionally it felt over-emphasised: yes they are constantly intimate, but it didn't always add to the story.
The writing was very nicely done. The reuse of words and phrases really drove home the right points and the language was well chosen. I never found this a distractor from the work which is good (and somewhat rare).
Overall I found Spar one of the better Hugo nominees, although I preferred Bridesicle. Definitely more interesting and memorable than the other 3.
One final minor irk, I found myself working hard to suspend belief enough for this one. The premise of the crash being so highly unlikely is fine. What broke it for me what that the alien and human are so perfectly matched they can share atmosphere/pressure/bodily fluids/injuries/environment for so long without any harmful effects... That seemed extremely unlikely. Add in the waste disposal system that apparently collects faeces (and urine, I can't recall), but not other discharges from the genitals? (How does it collect these when the alien is inside those orifices that discharge it anyway, wouldn't the alien get in the way?) Also, why build an escapepod for your spaceship that can adapt for the nutrition of any known alien, yet doesn't support even primitive communication? If you can determine all the chemicals to insert/remove from the environment of any alien then why not also have a minimal translator? (Mobile phones can do this now... So either the computer is powerful enough to work things out on the fly, so should be able to do some communication, or it isn't but has a catalogue of aliens... but not their language.)
1 - I can't help but consider that this was a mixture of lack of cerebral development and vague discussion of the physical. Seeing as her mental state is degenerate it can be helpful to have the mental/emotional fall apart. However, the physical was similarly disjoint, as a result the sense of time and change in physical behaviour didn't line up. Only the brief discussion of how she tried to track time and failed seemed to make any attempt to manage this. Ultimately I think the story would be stronger with a better sense of time passing, not necessarily in any measurable way for the character, but for the audience to perceive the transitions in state of mind.