Still a solid sci fi entry overall.
The process of the first two-thirds of the movie is really neat. The slow build-up of understanding the language is shown very well, with Adams giving a great performance. I also enjoy the interplay between her and Forest Whitaker, the career army man.
I take issue with Jeremy Renner's character. It is not made plain in the entire film why he is there. He's supposed to a scientist, and he is shown doing scientisty things, but they have no effect whatsoever on the plot. It might have been a good idea to pull back the focus to flesh out the mission a little more.
Once we get to the third act, the big sci-fi reveal happens. Here's the problem: you've already established a certain level of strangeness in the film, and this third act adds a whole new layer. It really pulls the rug out from under you. It might work for someone who was ready for that level of sci-fi, but I was not. It got really complex, really fast, and I felt whiplash while watching it.
It left a bad taste in my mouth, and looking back now a few weeks later, doesn't seem as egregious (hence the largely-positive rating). In the moment, it really took me out, though.