If you had your wish which part of thee Tolkien cosmos would you see made into a film?
Excellent question! As I think about it I believe the First Age would be the best of tales: the finest in 'Men' uniting with the supernatural nature of Elves to fight the dominance of evil.
The First Age is not the story of one saga, one mission that must succeed in order to prevail. There are many individual efforts and sacrifices, many wonderful fantastic feats that, in the end, come to naught. An Elven princess yields her immortality to unite with the heroic mystery of mortality.
One such human hero sails to the Undying Lands to beg the Angelic stewards of Middle Earth to intervene - as the alliance of Elves and Men is incapable of overthrowing the pervasive evil of Morgoth. His Elven lover acts as a navigator light to help him find the Island of Valinor. His plea is answered but he cannot return to the land of the mortals so he and his Elvish lover is transformed into a star - the 'light of our beloved Earendil.'
Sauron is a minor functionary who is subdued by the singing charms of an Elvish maiden while her human companion undertakes to seize one of the Silmarillion. Dwarves attack the Sindarin kingdom to steal a beautiful jewelry that they created for the king. That treachery sets up the long lasting enmity of Elves and Dwarves, only partly resolved by Legolas and Gimli in the quest of the Ring of Power.
The Valar facilitate the overthrow of Morgoth, who is banished to outer darkness. His lesser known lieutenant, Sauron, survives to operate in deceit and treachery in the Second Age. The valor of mortal men earns them longer life in an island paradise between Middle Earth and Valinor called Numenor.
The western most land of Middle Earth, Beleriand, breaks off and sinks beneath the sea, drowning Morgoth's fire pits and numerous evil creations... speaking of which, one of those evil creations was Orcs. Tolkien stated in The Two Towers where the Orcs came from; it was NOT broken Elves, a trap Peter Jackson fell into and is now rendered as fact. Elves were created with immortal lives, which Orcs never possessed; Tolkien portrayed the Elves as being of the highest nobility (which the Noldorin sullied.)
The passage in The Two Towers was apparently written out in a later rewrite and the origin of the Orcs will remain a controversy. Iluvatar created Elves (immortal) and Men (mortal). Presumably Morgoth desired to create a race and, lacking the highest divine skills, produced Orcs - as well as Balrogs, dragons and other abominations.
Another Valar, Aule, created the Dwarves, which displeased Iluvatar but, since they were not created with malice, he mercifully allowed to survive.
Sorry to take such a long slide. The First Age is masterful fantasy well founded in begrudging reality.