Middle Earth (Tolkien)

Short Answer: The Tolkien Reader... or The Kalevala and The Ring of the Nibelung

Peter Jackson's cinematic vision of the Lord of the Rings novels is beloved, and rightly so. His version of The Hobbit... less so, if only because taffy-pulling this one shortish novel into three epic movies was never a great idea to begin with.

But now Amazon is putting out The Rings of Power, a prequel series, set in the Second Age of Middle Earth.  I don't know to what degree the series is based on actual books Tolkien wrote, or if it is just pulled from various notes he made about his world's origins, but the Tolkien estate is involved, so that will help ensure that the show stays true to the sources, whatever they are. 

It is good that that Amazon is not trying to remake the books that Jackson retold, though. 

The very name "Tolkien" is somewhat synonymous with the concept of "epic" at this point, and many feel that the next Tolkien epic to tackle is his Simarillion. However, the estate is adamant about not selling the rights to that work or having it adapted. So it's really a non-starter to even discuss it.

I wonder, though, if they opposite approach might be tried-- instead of epics, maybe a series of stand-alone films could be assayed. The book The Tolkien Reader collects several of his shorter works, some of which seem adaptable: Farmer Giles of Ham, The Homecoming of Beorhtnoth Beorhtheelm's Son, and Leaf By Niggle... as well as The Adventures of Tom Bombadil, a figure who was in the Lord of the Rings books but cut from the movies because he mostly recited long poems. (Also in the Reader is On Fairy-Stories, but that seems more like an essay than a narrative.) There are other stand-alone works as well.

But an entirely different work might also be adapted. This is the work, the epic, that inspired Tolkien to begin with: The Kalevala. This is a Finnish tale with the scope of myth equal to that of the Norse tales, the Gilgamesh stories, or tales like the labors of Hercules and the Odyssey. The Kalevala is not all that family friendly, from what I gather-- but then neither are The Witcher or Game of Thrones, and not everything has to be at the Harry Potter level of family friendliness. 

And while the Beowulf story, which also inspired Tolkien, was made into a movie (that now, sadly, looks like a janky video game), the Ring of the Nibelung story, which Tolkien drew from, has not. The Norse epic was famously made into a very long opera series by Wagner (a set of four full-length operas!), and occasionally performed in marathon sessions by opera houses-- in German. This presentation is, well, not all that approachable to most audiences, and an epic movie series is warranted.

As for what Jackson's next fantasy-movie project should be? I think that the one who brought Gollum to life should also tell the story of the Golem.