The value of the History of Middle Earth is not just in the content it offers, but the historiographical approach to that content: Christopher Tolkien makes it very clear what comes from when and comes from where, what changes, what remains. It's a work that puts the conflicts, contradictions, changes and developments in evidence.
This work is the opposite. Not only it doesn't seem to care for the different context between the parts it incorporates, it also does not wish for the reader to care, either. I mentioned things are badly sourced, but it's also relevant to mention that the author takes bits and pieces from contradictory versions and stitches them together, with no warning to the reader. So that, for example, you have a Míriel who was in love with Pharazôn, but who was also unwillingly married, and whose throne was usurped by him. This could be a very interesting fan approach to the story; it irks me that it is not presented as that. In fact, this book is presented as a compendium of everything ever written about Númenor - but that is simply not true.
What it actually does is try to create a coherent narrative of Númenor from its creation to its destruction. That's a goal I can respect in theory, but it is, essentially, a fan work. It might be worthwhile for some, but it definitely isn't for me. I don't like the premise and I hate the execution (and I'm beyond disappointed, because I would have loved to have an actually useful compendium of Númenor information).
There are other problems, as, for example, blatantly incorrect quotes, such as the one on page 114. In "The Fall of Númenor", it reads:
"Of the life-span granted the Númenóreans, Erendis had once said that women 'became a kind of Imitation Elves (...)"
But the original text in "The Nature of Middle Earth" reads:
"As Erendis said later, [the Númenóreans] became a kind of imitation Elves (...)"
So not only the Fall of Númenor turns indirect speech attributed to Erendis into direct speech, it changes the very subject of the sentence (besides the incomprehensible capitalization of the adjective). This is one instance - the one that caught my attention the most; there are others, as well as a number of typos.
Not to be a complete downer, the illustrations of Alan Lee are gorgeous and particularly inspired. His art has a poetical quality that suits the theme brilliantly, and his depiction of some of the characters are particularly inspired. The profile of Tar-Ancalimë on page 118, for example, is particularly inspired, with fashion details that depart a little from the common sense and add new flavor to an otherwise familiar aesthetic landscape. His full-page, full-color illustrations are captivating; one can spend a long time looking at them. In my opinion, they're the true star of this edition.