I have read most of them. IMO, they feel un-finished, which is exactly what they were. I think they would be better if he just finished the tales, fleshing them out where they needed to be rather than remaining true to his father's notes/outlines. -- jim
I don't know. I thoroughly enjoyed reading The Silmarillion. Of course, that work publish dates much farther back than any of the others. It was a good read, and did go far to explain the mythic era that is often referred to tangentially in Hobbit and LotR trilogies later on.
I have the Silmarillion and Unfinished Tales on my shelf, but have done little more than flip through them. I did try to get through the abridged History of Middle Earth (the four volumes concerning the writing of LOTR) and found it interesting though I haven't yet completed it.
There is talk in the various LOTR communities that the quality of Middle Earth offerings may improve once Mr. Tolkien has departed. It may be argued that something similar has happened to the Star Wars universe in the wake of Lucas' sale to Disney. I don't mean the latest trilogy, which I personally find of poor quality, but the "Star Wars stories" - Rogue One, Solo - kind of suggest a post-Lucas universe won't be so bad. Chris Tolkien has spoken out against the quality of the Peter Jackson movies, and IIRC the fact that his father had already parted with the film rights was what led to them.
But, Chris Tolkien no longer serves as director of the estate, which may be why we're seeing talk of a television series. There have been video game licenses for a long time, and LOTRO (for just one) is still active.
If the television series is successful, who knows, perhaps we'll see an expanded universe type of book offerings from fresh authors. Personally, I'm finding fresh stories from the War of the Ring era (some of the quest line text from LOTRO, for example) more entertaining than the polishing of J.R.R.'s unfinished ideas.