There are some differences: a significant death is changed from an accident to cancer (probably a good change). The movie adds some extra international conflict

There are some differences: a significant death is changed from an accident to cancer (probably a good change). The movie adds some extra international conflict plot, which perhaps raises the stakes somewhat but seems like weak plotting, and the movie is more explicit about the aliens' motivations. The movie also drops some of the math/physics exposition, which would have enriched the film and given Jeremy Renner's character more to talk about. The story has a really good depiction of linguistic fieldwork and linguist elicitation sessions, while in the movie the linguists are too busy freaking out about the aliens to give a good show of the research methodology. I think the story is more successful, especially at jumping between the process of science and the grief-filled flashbacks; the film has to show the character's reaction to the flashbacks, which complicates the unfolding of the story. But I enjoyed the movie a great deal as well.