It isn't really game related in the sense of mattering for the game play but to me, a great soundtrack really makes a game stick for me. With that being said, RDR1 has one of the best soundtracks I had ever heard from a video game. I think it was damn near perfect and well fitted.
What are you expecting from the next game? A bit of the same? Maybe a few songs being the same with a remix? I would imagine that we do get some songs that are pulled from the last one only because they will be used to trigger memories maybe.