There are many flaws, such as Lule instead of Aule, or Ungoliant, the spider, becoming Ungoliath of the Underworld, but these are minor.
Technical aspects are well-executed, and there are very few flaws in the combat system (about the same as in Tolkien's works).
A new perspective on Middle-earth – yes, and that's precisely why many criticize it.
The sequel, "Adamant of Henna," turned out to be completely unsuccessful.
The style is somewhat too epic, and you get tired of reading it towards the end.
Overall, these are very different books – Tolkien's is a sad, philosophical saga, while Perumov's is a harsh combat story with some philosophical ideas.
I also liked "The Black Book of Arda," but if there, Nienna relies on beautiful language and a logical justification for a new perspective, then Perumov relies on combat, brightness, and the epic nature of the narrative.
And here's a joke on the topic:
A Tolkien fan ends up in Middle-earth. He sees mighty knights in mithril armor with huge swords, approaches them, and asks:
- Are you Gondorian knights?
- No, we are Perumovian hobbits.