Blue Valentine is a movie about two halves of a relationship: the first moment you fall in love with someone, and the realization that comes when everything is over and there's no chance of recovery. This is an extremely painful film with undeniably powerful performances from both Ryan Gosling and Michelle Williams. They go through both physical and emotional transformations during the five year period of the film: Williams from shy and adorable to cranky, dour and 15 pounds heavier, and Gosling shifts from charming blue-collar loverboy to disconnected father with a receding hairline.

The story is nothing new: boy meets girl and then loses girl, but this is about what takes place between the cracks. Relationships might begin virtually overnight, but it takes time for them to die, and that's where Blue Valentine turns tragic. Told in flashbacks from when they first meet to the death throes of their love, both the pounding heart moments and the bottom of your stomach falling out moments are here. When the story opens, Dean (Gosling) is awoken by his daughter Frankie (the adorable six-year-old Faith Wladyka), who tells him their dog Megan is missing. They go off to briefly look for her and return as Cindy (Williams) is fixing breakfast.

The film ambles along, painting a picture of a couple that's beyond the range of "comfortable," and there's an undercurrent that something is wrong between them, although the audience isn't sure what. Once the first flashback takes place, where Dean has moved to the city, found a job as a mover and is assisting the relocation of an elderly man when he catches his first glimpse of Cindy, the film begins to pick up speed. With each flashback, we see a couple falling in love, and a couple falling out of love, creating a dual-sided love story and a tragedy at the same time. But where you know the ending of Shakespeare's Romeo and Juliet, you have no idea where this is ultimately heading.

Dean makes the best effort he knows how to save their marriage: he books them into a seedy sex motel, and on the drive out Cindy runs into her ex-boyfriend Bobby while shopping for liquor. She eventually tells Dean, but this leads to an argument, and the trip doesn't go as planned. It's here where the movie teeters back and forth on the will they / won't they moment. They have arguments and disagreements that almost everyone has experienced in their own relationships, and these fights are so realistic that you might be ashamed to see yourself in one of these characters. I certainly was.

What's most impressive about this entire film are the dual performances of the actors, particularly Gosling who seems like two entirely different people depending on which flashback the film is in. Where Williams' Cindy is still somewhat hopeful about the future, Dean is beaten down by life, content to live it as a borderline alcoholic housepainter and father. You can see the pain in Cindy's face as she struggles to deal with this, and you also watch the tormented Dean vainly try to change ... which is something he's incapable of. He just doesn't have the tools or the vocabulary to deal with life any differently.

When the film ends, you'll see one of the most juxtaposed and emotional credit sequences ever put to film. I'm not sure how many people have been moved to tears by an end credit sequence, but director Derek Cianfrance, who premiered his 1998 film Brother Tied at Sundance, has opted for a Saul Bass-inspired sequence of images that are poignant and painful. Make sure you stay to sit through it. Blue Valentine is a great movie with what one hopes are not the defining roles from two of the best young actors working today, but that's how important and moving they are in this film. This has definitely been the most impressive and moving film I've seen at Sundance, and my hat is off to the actors and the director. This is nothing but a tribute to all of them.

Be sure to listen to our interview with Ryan Gosling, Michelle Williams and Derek Cianfrance right here.