The quality of the paintings are uneven, and each one has its favorite. Like many people, I find Hague lacking, but also Edelfeldt, who isn't bad but whose style is not unique enough in my opinion.
My favorites, on the other hand, are Howe, Garland, Nasmith, Lee and Galuidi. Garland, my favorite, has a unique and glowing, almost 'mystical' style that does the book justice. Howe's pictures are also intriguing and beautiful, and feel true to the book (and thankfully, he seems to dominate the book in terms of the number of contributions). Nasmith has some splendid landscape pictures, though his vision of the characters leave something to be desired (especially of a fat, distorted Boromir!) Galuidi's sci-fi, computerized style may not appeal to some, but I find them interesting. Finally, Lee's soft watercolors are very appealing, and his vision of the characters is near-perfect (especially Galadriel and Gandalf).
John Howe's have the vividity and beauty we expect from him, especially his outstanding picture of Gandalf that inspired the Peter Jackson movie's Gandalf; Alan Lee's are more ethereal and colorless, but still beautiful (especially his Luthien painting). Nasmith's are usually quite good; they're not as good as Howe or Lee, but head and shoulders above average. Goldsmith is fairly good, not exceptional.
Michael's Hague's are mediocre, lacking in imagination and sparkle but serviceable. Robert Garland's paintings range between the exquisite (his lovely "Smith" picture) and the cartoonish (his eye-popping "Haven" picture); the same is true of Edelfeldt, who is divided between bad and good. Phenix and Galuidi are just awful, garishly colored and totally unrealistic. Galuidi's Saruman looks like a picture for a D&D game, and his Barad-dur looks like a cheap scifi cover.
Each painting is accompanied by a relevant quote or piece of verse, usually an excerpt from the book in question (not just "The Hobbit" or "Lord of the Rings," but other books as well). There are some nice bits of artwork in this book, but only buy it if you can't find Nasmith, Lee, Howe or Goldsmith anywhere else.
