It is in keeping with Joe Swanberg's oblique approach that Happy Christmas, his latest low- key comic drama, was released in the US during high summer.

We wouldn’t want to think he was giving into the bourgeois demands of holiday programming.

Anybody blundering into his picture in search of reindeer and magic is likely to be disappointed. Happy Christmas finds the master of (the word is unavoidable, alas) mumblecore once again teasing ever so gently at the loose strands in relationships between hip young(ish) people.

One has constructed a 1950s- style Tiki bar in his basement. Another is struggling to start her second novel. A third is actually played by the actual Lena Dunham. This is a world every bit as formalised as that in Guardians of the Galaxy.

None of which is meant as criticism. Happy Christmas finds the director in sharp form and his cast bouncing off one another with energetic creativity. In a scenario that has resonances with this year's more mainstream The Skeleton Twins, the film sees a relatively stable couple (Swanberg and Lynskey) undergoing some disruption when a more uninhibited sibling comes to stay.

Anna Kendrick is wonderful – annoying, funny, hard to hate – as Jenny, younger sister to Kelly (Lynskey). Within minutes of arrivingat her relatives’ house, Jenny has escaped washing-up duties and headed off to a boozy party with her pal Carson (Lena Dunham). Mild tensions continue. She nearly sets fire to the house. She encourages the highbrow Kelly to write mummy porn. Some sort of uneasy romance kicks off.

So slight are Swanberg's films that it proves hard to resist focusing on what they don't do. Jenny is not transformed or cured of dissolution. She does not reveal any great hypocrisies in her in-laws' relatively content life. Nobody makes any huge closing speeches. The film potters amiably and affectingly towards an ending open-ended enough to be mistaken for real life. It's good to have Joe around.