If you have friends that might be into minecraft like games, then Terraria will be one of the greatest games you'll ever play (it was certainly the case for me). The exploration, boss fights and sheer enjoyment of finding something new makes this game a blast with friends. I highly recommend it.
Witcher 3, as
@Tracer_Bullet said is definitely one of the best RPGs ever made. Its a ride from start to end, and will keep you glued to your screen throughout. Its not exactly a laid back game though, but a thought provoking one for sure.
RDR2 is the one I would pick, if I wanted to relax with a single player game. Even now after completing it, I still go back from time to time to experience the calmness and the serenity in its exploration.