It has to be near-impossible to have the job of writing a one- sentence, intriguing byline for a movie like this that also doesn't spoil the story line.
Then people go to the movie expecting Transformers VII and get a fascinating, beautifully character-oriented film like this and are either 1) angry because they're action / explosion fans or 2) upset because they had different expectations - even if they end up liking the film.
If they marketed it as a relationship film, people who went for Sleepless in Seattle would be angry about the sci-fi. It's a no-win scenario for this type of script.
I'd have to argue that it's properly billed as sci-fi in that the circumstances create the context for the story to unfold as it does, and they are "sci-fi" circumstances.
In my mind this movie was very similar to Monsters, which was also mis-marketed and was a beautiful character-driven film.
If you liked films like Monsters or Solaris (Clooney) then you'll probably enjoy this film's pace and themes.