The Darkest Hour- Solid, if a little dry depiction of politics on the UK side during Operation Dynamo during WWII. Phenomenal performance from Gary Oldman, who took home a well-deserved Oscar for his work. The rest of the film is a pretty good, if unspectacular history lesson which will probably find its most natural home in schools. A decent docudrama about a pivotal moment in the war, with great performances and strong production values, but it falls a little short of being as dramatically involving as it wants to be.
I loved this movie. Even as someone versed in WWII history and politics, I learned some about the degree of hurdles Churchill had to overcome when he came in to replace Chamberlain. It was very well done, and, as you said, a spectacular performance from Oldman.