The Fortress (남한산성/南漢山城) is not the best movie for a brief escape from reality. It can be a rather depressing movie, with a limited number of action sequences, so it may not be that appealing to a modern audience. It may be too dreary even for a Korean audience, but I don't know what the Korean reviews of the movie have been like..
The movie is critical of the hypocrisy of the royal court (and of most officials in general). The pro-democracy sentiment expressed briefly by one of the characters in the movie was perhaps anachronistic, even if we might agree with it. (And it is this sentiment which leads to the small emotional pay-off at the end of the movie.)
Some may think that the characterization of the minister of the interior Choi Myung-kil and the minister of rites Kim Sang-heon is inadequate. I thought the conflict (and limited cooperation) between them was sufficient enough to draw a contrast between the two men. (Does the original novel pay more attention to court intrigue and conflicts between the various officials?) Their different understandings of what duty and loyalty require are the engine of the story. (Is the movie, or novel, an adequate representation of the neo-Confucian mindset, though?)
The movie does raise an important moral question: of the prudence for waging a just defensive war against an invader when the defeat seems more likely than not.
Given the historical circumstances of the story, watching the movie can be a bit of slog, and the character arcs of the two officials may not be enough to keep most people's attention.
Still, LBH should do more saeguk -- he's good in these roles.