Frankly, it's got it all: expert casting, great dialogue, fascinating history, powerful dramatic encounters, and yes, a fine love story.
Good thing this is only a blog, because I can talk about the backstory and the making of for hours. This was a labor of love for producer/director/star/left-wing-extremist Warren Beatty; good for him that every frame of the film shows his deep love and care.
For those that don't know the story, the film follows the radical socialist/communist movement in the US in the late teens, from before to just after The Great War. That may not sound like the prescription for a blockbuster flick, but by focusing on the marvelous characters and lives of those promoting that movement, the movie is alive with emotion and intellect. It focuses on the life of journalist (or politician?) Jack Reed, one of the few US citizens to be so respected by the Soviets as to be immortalized with burial in the Kremlin Wall.
Can you watch such shenanigans for three hours? Believe me, it's absolutely compelling. And by the time that you're not sure just how much more infighting between the Communist Worker's Party versus the Communist Labor Party (splitters!!) you can take, you find yourself swept away in a revolutionary montage storming the Winter Palace with Beatty and Diane Keaton as they overthrow the Czarist government all to the driving music of the Soviet Army Chorus singing the communist party anthem, The Internationale. (again, believe me, it's absolutely thrilling.)
Special mention must be made of Jack Nicholson's bitter portrayal of Eugene O'Neil and Maureen Stapleton's fanatical Emma Goldman mother-figure. But there are so many interesting performances and details - e.g. When Jack Reed is supposed to be interviewing the Russian parliaments prime minister Kerensky, the actor is actually Kerensky's real grandson; WWII survivor and author Jerzy Kosinksi portrays bolshevik politician Zinoviev; etc; etc; - that the sum is a profoundly memorable experience.
And finally, regarding the cold war against Soviet totalitarianism, won a mere five years after the film's release, Beatty (and Reed) may just be quoting Tom Lehrer, "though they may have won all the battles, we had all the good songs!"