What makes LotR hit like a Howitzer shell to the gut is not the reader's knowledge of the background mythology. It's their knowledge that it is gone forever. As Douglass Parker wrote in 1957, "Tolkien’s whole marvelous, intricate structure has been reared to be destroyed, that we may regret it."
Tom Emanuel
LotR is Tolkien's masterpiece. The experience can be enriched by reading The Silmarillion too, absolutely. But my dad didn't have the Silm when he read the Ballantine paperbacks in 1965 and felt such immense grief at the ending that he immediately picked up FotR and started over. He didn't need it.
Tom Emanuel
Getting exiled from the Tolkien fandom because I have in fact read the Silmarillion but still prefer LotR.