Like Chinner said it didn't translate well to a game at all. A game is supposed to be fun and provide you with many fun things to do, but making a true wild west game by nature doesn't provide many chances at that since it was mostly desert with a few very small towns. Herding cattle, taming wild horses and hunting animals is not fun, nor is playing horseshoes.
Yeah, the little time wasting tangential stuff in most open world games frequently turns me off, but I'm glad it's there for people who really get into it and it shows a certain commitment to details. Most of them are like city garbage collection, I'm glad it's there, I'm glad it happens, it's irritating if it stops working properly, but it's not something I'd care to do or think about if I don't need to. I usually find one or two I really enjoy and ignore the rest. In RDR for me, that was doing Bounties and horse wrangling.
I do think however that the period could have translated well. The game takes place right before WWI, there was a lot of material they could have worked with. They wanted to tell a small story though, and in the confines of what was then a culture on the way out, and thrown in Hollywood Western flavor. I hadn't really thought of the game as a missed opportunity before, but I guess I've always just thought the game worked better as a Leone homage more than a historical sandbox.
You can get 100% in 30 hours, less if the hunting challenges weren't entirely based around luck and whether those fucks wanted to spawn or not.
I should partially take back what I said though. Sleeping Dogs had less content, that only took me ~22 hours to 100%.
Oddly enough, I enjoyed Sleeping Dogs more.