I finished story mode myself.
The Negative: I agree with the Horse riding be too long, and boring. The Beginning being also too long, and boring. The controls are frustrating and clunky. I hate having to get your rifle out of the horse over and over again. I also did not like the attempted RPG shit like eating, feeding+brushing your horse. To me, it didn't work.
Positive: The story was really great. Maybe a little too long and with some less interesting characters, but the dialogue between Arthur, Dutch and John was great. The graphics are phenomenal. Some of the levels are epic, I especially like the huge battles like the one with the Indian (Rainfalls?).
Overall I though it was a flawed masterpiece.
Has anyone played the updated online mode yet? I'm a huge GTA online fan (got the flying Deloren with missiles, yeah I'm that guy lol) , but I wasn't sure about it working on RDR2 with the clunky controls, and overall slower pace.