Saw it over the weekend. I enjoyed it, but it fell a little short of fantastic. The script/story left a lot of unanswered questions or, rather, buried them under an artificially-sweet emotional ending. I read Chiang's short story the following night and it was much tightly executed and delivered the idea more effectively.
It was a beautifully-made movie though. The effects were believable. Adams was good. The score was great.
-edit - How can anyone not like District 9? It was a little heavy handed with the apartheid allegory but otherwise I thought it was perfect.
I also saw the movie and then immediately ordered the short story collection. I was able to read it and then see it again in theaters with some other friends. I did enjoy the short story, but it made me appreciate what the film did and the changes that were made. The short story is a more straightforward narrative and solidifies the scientific theory behind the written language. It does flip around in the timeline, but there is no twist like in the film. The movie builds up the reveal of the aliens and then mixes her learning the language with a corresponding decent into madness until she "gets it" at the party scene. Re-watching the film made it more clear that she isn't seeing other parts of her timeline until right after she starts to understand their language. The first time watching it, it just seems like exhaustion combined with flashbacks of her dead child. Watching it again shows her mental breakdown from experiencing the visions with a girl she doesn't know. At the party scene, you see the wave of various emotions just hitting her. The short story still has a lot of emotion in it, but the film does a much better job of the viewer feel the emotional weight of her realizing that the girl is her daughter and that she will die, as well as the fact that she is the key to stopping a world war.
There were quite a few other smart changes that I thought the film did. The short story has 112 "looking glass" objects just appear and are only 10' by 20'. By making there only be twelve mysterious (and massive) objects, the world war plotline is introduced and makes Louise much more important. The film also has a bomb killing one of the aliens. At first you think Abbott is trying to point at the bomb, but after seeing it, I think he was trying to get one last way of getting her to understand their language by having her touch the barrier. Either way, it seems like Abbott knew about the bomb and chose to die in the blast anyway to save Louise and Ian and fulfill his story line. It makes the decision that Louise makes to be with Ian knowing that she will lose both him and their daughter more understandable. The short story does a better job of explaining that even with the understanding of the future, it's still your duty to fulfill your part in the grand performance. I also like how the film gives sort of a purpose to why they came. They needed to unify humanity so that they can give us their technologies that we will use to help them in the future. It's a bit vague, but the short story says that the purpose of them appearing in glass objects on Earth is not known in Louise's lifetime and they don't give humanity any new technology.
Anyway, I think people should see the film, read the short story, and then re-watch the film again. The short story really does a great job of explaining the alien language and how the circular timeline works, but the film tells a much better story. I wish there could have been another five minutes of "science" in the film to help fill in the apparent plot holes which are explained in the short story, but I understand why they would leave it out for pacing.