This is an excellent film. Not usually a western fan, I am now a true-believer -- fan of the genre, of Wayne and O'Hara, and even, reluctantly, John Ford. Rio Grande captures the spirit of heroism that colors most of John Ford's best work. Strong personalities pursuing their values with a philosophical issue dividing them: it has an excellent, concise plot, well-developed characters, and boasts fantastic acting. Ford even shies away from allowing the scenery to star in the picture, which is a welcomed departure. With monuments like Wayne and O'Hara one does not need Monument Valley (this writer humbly submits.)
There is a profoundly moving scene in which Kirby and Kathleen York's entire relationship is summed up in the mere singing of a song (by the unforgettable voice of Ken Curtis) and O'Hara and Wayne's excellent acting -- hardly any dialogue, no flashbacks. It has to be cinematic moment for the history books... it is at least in mine.
By the way, avoid the colorized version if possible. Among other distractions, it makes John Wayne's hair look like instant brownie mix.