When you are used to get great things, and you expect them again, the average won't satisfy you.
This happened to me when I saw this Danish movie. As a person who adores movies from Northern Europe, especially when it comes to children in movies (regardless if it is a kid's movie or an adult drama with kids in important roles), and finding Danish movies usually even better than their northern neighbors, I expected too much.
Oskar & Josefine is made after a TV serial as a sequel. Though it is more than obvious throughout the movie, there is no problem to understand the plot because of the introduction sufficient to those who haven't seen the serial (like me).
The serial was a fairy tale for younger kids. The actors in the movie are a bit older, and so are the characters, they are a boy and girl who are in love and going on vacation together (though they go to boy's grandparents and though it is Denmark, we can assume that the authors aren't persuading us they are 12). But the plot is again a fantasy in a fairy tale style, so the target audience appears to be rather unclear. Kids who watch the movie must have some knowledge of history and other subjects (not easy for 9 or 10 years old, who would maybe otherwise be interested in such a fairy tale), but the knowledge of characters is also sometimes surprisingly weak. Just for example, Josefine, a girl old enough to go with her boyfriend on vacation, and who has already saved Jesus and Christianity (in serial) doesn't know what antibiotics are.
Movie for younger kids, though a fairy tale, can still be enjoyable for the whole family. Ronja Rövardotter maybe pushed the standards unreachably high, but it's not the only good one. This one is watchable, but nothing more.
I have another problem with Oskar & Josefine. Teenager traveling through time in North European movie reminds me in a second on Sofies verden, unbelievably intelligent movie (for a bit older audience, again the one very suitable for adults as well), who succeeded on different levels so can be watched as an adventure (from early years, though preteens might be bored), SF (not for hard-core fans), semi-documentary (a lot of facts that can make adults repeat their history and philosophy lessons) and a real art movie with references from Carroll's Alice to Fahrenheit 451. People who haven't seen Sophies verden are in advantage when watching Oskar & Josefine, because they won't compare these two movies (and the latter is weaker in any aspect you analyze).
The choice of actors was not perfect either. Not only age-plot relation, but their acting wasn't impressive as Danish (and Scandinavian) kids usually act. There is a strong hollywoodisation of Danish cinema in new millennium. But the work with young actors has never lost its quality that hasn't been achieved almost anywhere else. Pernille Kaae Hoier is no Sarah Juel Werner or Line Kruse - but this role would be perfect for Julie Zangenberg, whose age would fit as well. Instead of Mikkel Konyher I would prefer to see Adam Gilbert Jespersen or Anastasios Soulis (from Sweden, but borders were never a problem in North Europe), however as a couple Julia Krohn and Bernhard Naglestad from Norwegian movie Ikke naken would fit the best.
On the other hand, adult actors played just the way this movie needed. Average photography and music won't be remembered after the closing credits.
So if you are not familiar with Danish movies, don't start with this one. You might give up with further explorations, what would be a great loss considering how great Danish cinematography is.
