The single player is timeless mate. Genuinely one of the best stories in gaming. Online is pretty quiet yeah but nobody plays RDR2 for the online anyway. Just take your time with the campaign and soak it all in. You will not regret it.
Yeah, absolutely still worth it. Damo finally started it last month and I had to stop myself giving him spoilers every five minutes. The thing that gets you is how alive the world feels -- strangers showing up, weather changing, all the small details that most games skip. Still one of the best things I've played.