There's not much to say about Song to Song that I haven't already said about Terrence Malick's previous two films, To the Wonder and Knight of Cups. If those films didn't endear you to Malick's increasingly experimental cinematic input, this one certainly won't.
Here we have the same setup as the two predecessors: take today's hottest actors (here, Ryan Gosling, Rooney Mara, and Michael Fassbender), have them improvise their way around various spaces as cinematographer Emmanuel Lubezki shoots them beautifully, add a generous portion of voiceovers, and edit it all into a poetic mishmash where narrative is completely out the window. (For what it's worth, Song to Song concerns a love triangle between musicians Gosling and Mara and music producer Fassbender, with a few other famous faces wandering in and out of the movie.) But whereas To the Wonder and Knight of Cups were salvaged by poignant autobiographical elements, I'm not sure how much of Malick is even in Song to Song, except that the film is set against Austin's music scene, and Malick lives in Austin.
The main reason Song to Song didn't work for me as much as the previous two Malick films did is that I found the cast to be weak. Gosling's good – his wry, no-nonsense acting style is a great benefit to the film. But Fassbender, who I usually like, is too stagy and serious – scenes in which he's supposed to be sexy only come across as sleazy. And Mara is one of those actors who simply cannot hold my attention. She's mousy and miscast.
There's a lot more in-scene dialogue than in the last two films, and the music from various live gigs adds a little energy, but Song to Song is, frankly, boring. Even as someone who can find something worthwhile in even the most ponderous of Malick's escapades, I was mostly just checking my watch.