Is RTL a more mature sounding album than MOP?
When I listen to RIDE THE LIGHTNING I hear an album with real vibe and themes of trench warfare and lovecraftian horror and it feels like an album made for aficionados of heavy metal.... when I listen to MASTER OF PUPPETS I think of adolescents sitting in their bedroom who don't want to do what mom and dad told them. It sounds more like an album made for a younger audience than RTL.
I know that's a silly reductionist way to put it, but just the themes and delivery of the songs sounds more mature on RTL to me.