“Happy Christmas” is a slightly above-average example of a kind of movie — and of a trend within movies — that needs to be encouraged. Directed by Joe Swanberg, it’s not quite in the league of his previous effort, “Drinking Buddies,” but it exemplifies the same appealing style, which strives to show life as it’s lived and people as they really talk and act.

This is how uninflected and natural “Happy Christmas” seems: After seeing Swanberg and Melanie Lynskey play a married couple in the movie, I checked online to see if they’re married in real life. (They’re not.) In the film, they’re an artsy couple in Chicago, getting by with reasonable success. The big event is that the husband’s flaky sister comes to visit — for an indefinite stay.

The sister is played by Anna Kendrick, who is at her best in a Swanberg universe — fuller and more inventive here (and in “Drinking Buddies”) than she ever gets to be in her big-budget appearances.

The rest of the movie plays out as a seemingly loose series of events, showing the couple’s daily life, the sister’s tendency to find trouble and the influence that the mature and the immature have on each other.

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Actually, “Happy Christmas” is a little too loose, a little too unstructured. Swanberg doesn’t provide enough tension and drama between the characters, and so much of the dialogue, which is improvised, sounds like vamping. Lena Dunham, who plays the sister’s friend, is particularly annoying.

The movie’s flaws are compensated by two things: Swanberg has an instinct for when to cut. And his movie captures natural moments between people that somehow elude other filmmakers. For those reasons, I’ll see any movie this guy wants to make.