SPOILER ALERT (who would guess)
First I want to establish that I, like most gaming geeks, loved the living hell out of RDR. The sheer amount of things done right in this game is jaw-dropping, trumping even Niko Bellics adventure in terms of the abundance of elements it nails. Shootouts, for one, are far better handled here than in GTA IV. But what GTA IV had which RDR doesn't have, is an ending which does NOT piss all over everything the story had been trying to establish.
Throughout the game we are faced with the idea that the simpler times of the old west are coming to an end, that civilization and industrialization are coming to stay.
One of the biggest themes of the game is nostalgia for these primitive times, despite how barbaric they were. John Marston is very much a relic of these simpler, more brutal times. Another theme is the question of how wether or not true REDEMPTION is possible, personified in this case by John´s attempt to escape his bloody past.
Close to the end of John´s adventure he is finally - after killing off the last of his old gang - granted permission by the FBI to return to his family and attempt to rebuild and REDEEM his life.
He reunites with his wife Abigail and his son Jack at his farm, where he spends the next few "missions" trying to make ends meet, both with regard to his economical situation and his family life. In his dialogues and attempted bondings with Jack, it becomes clear that he wants his son to become a better person than he was (a typical but, in this case, functional element of a story). Just as things are looking up, the Marston family one day spot the army riding towards their peaceful home. The scene that follows is the game´s dramatic climax, as the Marston family desperately chip away at the relentless attack, shooting soldiers left and right.
After a while, Marston (presumably, but in all likelihood) comes to the realization that he cannot escape his past, and that the only way to give his family a better life is to sacrifice himself.
So, running into the barn, and sending Jack and Abigail off on a horse, John Martson calmly steps outside the barn, where he is faced with a huge amount of troops and is gunned down, taking six soldiers down in the process. This is obviously a very emotional moment in the story.
Hearing the gunshots, Jack and Abigail ride back to the farm, where they find John´s bleeding corpse and cry over it.
John probably realized that his REDEMPTION would be not through himself, but through his son, Jack. His son would live a good and honest life, and that would redeem John´s dishonest and brutal ways.
If the story had ended there, all would be well. We would have a satisfying climax to a great game.
But, as our hero is dead, we would not be able to further explore the gameworld like in other Rockstar sandboxes, and dumbasses would complain on the forums until the end of t3H 1nt3rwebS. So, in a decision that can only have been made out of anxiety to please this crowd, Rockstar San Diego made it so that after Marston´s death, we are taken 3 years into future. Jack is now a grown man, and has inherited his father´s variety of guns as well as his side-mission assignments and money. The player is now free to ride around exploring the world, basically being a bandit just like John. His father would be proud, as now, everything about Jack becoming John´s redemption is almost ruined. It is never addressed how Jack now surely must be the biggest disappointment since the Star Wars prequels.
And it doesn't stop there. When you discover it in the world, there is an epilogue mission where you hunt down the Federal Agent responsible for John´s death to gain revenge. You confront him on his hunting trip in Mexico. The agent then claims that "your father killed himself with the life he lived", something which - despite this agent being a total bastard - is kind of true.
Nonetheless, a duel ensues and Jack kills the agent, triggering the credits.
That´s right, technically, this is the true ending of the game.
I´m sure violent revenge was just the thing John wanted his son to do. Redemption and all that.
Thank you for reading.