I don't like Westerns. I let this game sit for a year before picking it up a couple of weeks ago. I can't stop playing it. Aspects of it feel like an apocalyptic game, and I'm not talking about the zombie DLC -- which is inspired in its own right.
There's so much to do. There are recurring minigames, but many hours in I don't feel like I'm running into fetch quest type of scenarios.
The usability is amazing. The cover system could be a bit better, but there is one, as well as options for aiming difficulty. Although there's not a de facto leveling system, the items you acquire convey an organic sense of leveling. The menus and maps are easily navigated. These enhance gameplay.
I loved Far Cry 3, but prefer this game for its depth and variety. I liken the two because of the bounty hunter and hunting missions. Far Cry 3 had me wanting to see the outcome of the story, particularly after the early demise of the best antagonist. I don't want Red Dead Redemption to end, and I'm saving the DLC as dessert.
I believe you've already gotten your answer from everyone above, but let me reiterate: This game, whether you enjoy westerns or not, is enjoyable for most that play it. I don't like westerns, and yet I would easily rate this one of the best games of this console generation. The world is beautiful, but not just in an eye-catching sense. It lives and breathes like an old western. Random events take place for no reason other than to immerse you into the world. Animal personalities have never been done so well (just look up a video of cougars and you'll understand). It's fantastically well made.
If you like sandbox games in the slightest, I'd recommend giving this one a shot.