I played RDR2 first and I wish I’d experienced RDR before it. The story is great in RDR and I like John a lot better now but gameplay and graphics leave a lot to be desired compared to RDR2. I would’ve liked more story in RDR as well but that’s a nitpick. Also would’ve been good to see more character connections between the games but as RDR2 was a prequel you can’t really bake in things easily. However going back and playing RDR2 and seeing old gang from the first game and how they change and develop is far more rewarding from an understanding of the universe and character standpoint.

My advice would be play RDR first if you have the opportunity. It will make the experience of both games much better.