Before watching the movie:
I’ve seen a handful of episodes of the series, but I couldn’t say I know it very well. As I understand it, the book this is based on is intensely serious, the movie is a dark comedy, and the series started out almost at Hogan’s Heroes-level hilarity before getting even more morose than the movie (perhaps because the series lasted so long the war was longer for them than in reality).
So I guess what I’m expecting here is a cynical but amusing picture of the Korean War. I don’t know what characters from the series are there, and which are played by different actors, but I don’t know half of them anyway. There’s probably going to be a lot more money on the screen than a television sitcom can afford.