Nailed it.
The story, the setting, the characters...every single part of RDR was as near as you get to perfect. What really sells it though is, as the article so rightfully pointed out, the understanding you have of being part of a changing world. Marston is living in a world to which he no longer really belongs and the way Rockstar managed to make you really feel that is downright amazing. And the ending. Sweet jesus the ending. I could not imagine a more absolutely perfect ending.
Everyone goes on about how they finally brought the western genre to games successfully, but what few stop to consider is that they didn't just bring the western to games, they brought games to the western. Would RDR have made as good a film or as good a television series as it did a game? Absolutely not.
The zombie thing was really well-done too, maintaining a strong western feel while adding horror elements and a compelling storyline. And the sidequests...that bigfoot thing fucked me up in ways that few games have managed.
Multiplayer? What multiplayer? RDR didn't have multiplayer. I have no idea what you're talking about.
Now my grinchy moment: Brotherhood made the list? Really? It's just a browner Assassin's Creed 2 with more random, meaningless side quests. AC2 remains one of my favourite games and I was really excited to play Brotherhood, but it just feels cobbled together. The multiplayer is by far the strongest part of the game, but everyone keeps acting as though the single player is some great revelation. The game (ESPECIALLY the animation) is buggier than AC2 and considerably less polished in terms of general production values. The combat is a little better (not HARDER, BETTER), but the story is awkward and samey. First there's the issue of an established assassin doing random chores as a tutorial (this made sense in AC2 where you were a teenage. It makes much less sense in Brotherhood), then there's the generic feeling of the game (go to this brown area of the town, climb this grey building, kill this random guy you heard about five minutes ago), and finally there's the general lack of any feeling of momentum in the story. AC2 gave us several amazing (AND COLORFUL) locales, interesting things happening in them, and it just felt like each mission was considerably more special even when they were mechanically pretty samey. In Brotherhood, they don't seem to do much to mask the sameness and even the awesome things seem pretty humdrum since they try to cram SO MANY OF THEM IN EVERYWHERE what with the new items, new skills, new mechanics, and new vehicles. The vehicles are a great example. In AC2 you drive a wagon and then there's a big epic moment where you use a flying machine. In AC2 there are FOUR vehicles, they're treated like collectible side quests, and the very first one involves a MACHINE GUN. And I don't even know who came up with that Romulus idea. It gets introduced as a complete non sequitur -- a bunch of random crazy people jump you, so you kill them and decide to go underground into their ancient lair? And the armor of Romulus? Really? That's your replacement for the armor of Altair, which had an actual continuity in the series in addition to just being the best armor.
Brotherhood felt more like a parody of the series than a part of it.