Nolan's best film, and its on par with Saving Private Ryan. Don;t be worried its not rated R, it did not need to be, its not about the horrors of war its about the tension and terror of soldiers being stranded, surrounded and the underlying doom they must have felt being trapped in Dunkirk.
IMAX is highly recommended for this I saw it on one of the 70mm showings and its gorgeous. This will win A LOT of awards come that time, he made a movie with 2 total pages of dialogue (there might have been more maybe), and it kept you glued to your seat is a feat on its own.
Small edit. This is not a movie for speeches or heroic last stands or anything of the like. Its as fact based a war movie as I have ever seen. Some of the negative reviews have pointed to this as a bad thing, but I think the lack of emotion you would expect from a war film was a fresh take on it. Its not documentary level or anything however.
Not sure when I will get the clock ticking from Zimmers score out of my head.