Ok, first of all: this is a good movie on its own merits. It's got good writing, good pacing and is engaging for what it is. But odds are you're not going to like it if you know your history, and if you don't, this movie isn't going to teach you anything.
The problem, however, is that it tries to deal with two different subject matters at once. It tries to be about the Battle of Narvik, but it also tries to be about the fate of civilians - in particular it tries to show how people could be pushed to collaboration, even though there's only the one example. And this seems to be the main focus of the movie. Had the title been more honest, this would have been a better movie. We are only offered a couple of skirmishes to represent the actual battles, and these skirmishes lack any sense of scale. The landing at Bjerkvik, for example, is represented by a small handful of Norwegians along with 4-5 French and 2-3 Polish soldiers, fighting against 5-10 Germans defending a single railway gun which looked to be no heftier than an 88. And this was the biggest engagement shown.
I don't think I saw a single British soldier in any of the skirmishes - there were a total of three - and the entire Allied operation seemed to hinge on the ability of a single woman to gather intelligence for two British consuls hiding in a shack. If that sounds silly it's because it is.
In the end, I give it a 6/10 because it's an engaging movie - but also quite the disappointment. Had they ommitted all the "battle" scenes, focused entirely on the female protagonist and her struggle between doing right by her family or right by her country, and not pretended this was a movie about the Battle of Narvik, this would have been a better movie.