The Silmarillion (1977) is to The History of Middle Earth, what Lamb's Tales from Shakespeare is to Shakespeare's plays.
This describes my (elsewhere elaborated) feelings about the net effect resulting from the extensive process of selection, compression, subediting and forced-harmonisation that was imposed on JRR Tolkien's original material by the 1977 Silmarillion.
(My understanding is that Christopher Tolkien did the selection and ordering, and Guy Gavriel Kay did line-by-line editing/ ghost-writing.)
Lamb's Tales from Shakespeare has some literary value by the critical consensus of the past, and was apparently popular with our ancestors. But there is a heavy price to pay in literary terms; as may be seen from its presentation of Portia's courtroom speech from The Merchant of Venice:
The importance of the arduous task Portia had engaged in gave this tender lady courage, and she boldly proceeded in the duty she had undertaken to perform. And first of all she addressed herself to Shylock; and allowing that he had a right by the Venetian law to have the forfeit expressed in the bond, she spoke so sweetly of the noble quality of MERCY as would have softened any heart but the unfeeling Shylock’s, saying that it dropped as the gentle rain from heaven upon the place beneath; and how mercy was a double blessing, it blessed him that gave and him that received it; and how it became monarchs better than their crowns, being an attribute of God Himself; and that earthly power came nearest to God’s in proportion as mercy tempered justice; and she bade Shylock remember that as we all pray for mercy, that same prayer should teach us to show mercy.
Similarly; the 1977 Silmarillion is a partial, distorted and flattened 'nursery' version of JRR Tolkien's primary writing; which may be found in Unfinished Tales and the twelve volumes of The History of Middle Earth.
It is not that The Silmarillion is bad; but objectively, it is not a part of JRR Tolkien's oeuvre.
In all honesty; The Silmarillion should not be published and sold under the name of JRR Tolkien; but instead as a sort of 'condensed book' reduction and rewrite of the primary texts.