The movie was surprisingly good.
In case you don't know, the premise is that Doug (DT) and Abby (Rosamund Pike) have three children, Lottie, Mickey, and Jess, and they are currently separated and going through a divorce which they haven't told Doug's family about. Doug's father Gordie is dying of cancer, and they decide to travel up to Scotland to attend his 75th birthday party, trying to hide their difficulties and their divorce through the weekend, because Doug doesn't want to upset his father and wants him to live the rest of his short time thinking that his son and family are doing well. On a meta level, the children were filmed by letting them act they way they wanted to, and the adult actors had to react in character to them. (That's what I heard anyway, and that's a terrible paraphrase of what I heard.)
With a description like this, I expected this to be a slapstick type of movie, with instances of the children nearly revealing the divorce to Gordie (or to Doug's brother Gavin and his family) and Doug and Abby working to cover it up, ending in feel-good, "Oh, we really actually do love each other" reconciliation, but it wasn't like that at all. This myth was dispelled in the first few minutes of the film, as Doug and Abby are trying to get the kids loaded into the car to leave on time, agree on a path and a timetable for traveling, etc., without arguing - and failing, on all counts (succeeding at their tasks and avoiding arguing). Each of the family members are painted well, so you can see exactly where they're coming from, why they're reacting the way they do.
The thing that really made this movie, though, was the situations the characters got into and the dialogue. They weren't designed to make you go, "Oh, such precocious children, how adorable!" They were realistic, though of course things start to head down the bit unlikely path as events start to spiral out of control. But it just amazed me how much I laughed during this film. This is not the kind of film I normally watch, and when I do, I rarely react, but I really laughed. Here's another point in its favor. As normal with non-sci-fi Tennant shows, I sit down to watch them alone, with my husband at his computer playing video games and whatnot. He might listen in, but he doesn't watch or pay close attention. Within the first few minutes, he was laughing, and after about a half an hour, he was watching. And at one point (if you watch the movie, you'll know which one), he berated Gordie with "You bastard!" and laughed. If this type of movie catches his attention, it must be good.
So, short answer: I recommend this movie. It's fun and entertaining, and heartrending in the right places. Go catch it while it's in the theaters. If only to find out why this is the poster for the German version.