Just a few quick thoughts. This is probably the first bona fide masterpiece I've watched since The Cloud-Capped Star. I'm not giving away huge spoilers but if you'd rather see the movie first before hearing certain plot points, please see the movie ASAP! It's worth it ...
The moment when Marty (Power) & Mary (O'Hara) first meet is amazing. His marriage proposal to her, later in the film, is equally amazing. It was while watching this that I realized the extent to which John Ford's direction of actors is so deliberately his own. The proposal takes place on a porch bench. Up until this scene in the film O'Hara hasn't spoken a word, steadfastly so. Marty decides he's going to give her one last shot, he wants only two words from her: "Yes or no." (You can guess what she says out of the blue.) Ford has his actors sit straight, staring ahead and not really looking at each other, instead looking in the direction of the camera, eyes wide. They only turn to each other when their animated fury and passion insist on it. It's a moment like this--a moment when the turning of the earth is felt in the lives of the characters--where Ford always has them look off, gaze away from the substance of the illusory material life the film-narrative represents, and gaze into the suggestive unknown in the camera's offspace. The same effect is given in Ford's work within the frame when characters gaze at signs of dead loved ones, whether it's Nathan Brittles at his wife's grave in She Wore a Yellow Ribbon or where Spencer Tracy's character looks at (I think) his late wife's portrait in the hallway.
The night when Marty & Mary's son is born and the (much later) Christmas night when West Point cadets crowd Marty's home are linked by the same song, which takes on multi-faceted resonance due to the circumstances around each social celebration, where loneliness is the acutely felt elephant in the room.
Maureen O'Hara is immortal, in case you didn't know. She counts as one of those cinema axioms, I'd say. There's a scene where the cadets are rushing off and she tries happily to swat one on the behind, and basically misses, and it's in the graceful arc of her swing, as well as the camera nonchalantly capturing her failure to really connect, that we get a glimpse of what Serge Daney might have referred to as the quickness of Ford's camera, where the blink of an eye brings you the world in a Fordian frame, but it's over before you can feel and realize it simultaneously. Which is why time crushes all, and why for Ford life in all its vibracy is still dwarfed by death.