I still refer to Maurice Hinson's book from time to time. However, the information given is rather sparse. On Iberia, for example, it starts off by listing the 9 pieces, then there are only about 5 sentences, which I quote:
"This pianistic marvel is Albeniz's masterpiece. The pieces are evocative of Spanish scenes and landscapes and they blend Liszt with newer and more suggestive elements of the best French music of Albeniz's times. Enormous technical demands. [Level of difficulty:]D[ifficult]."
Hopefully, this will give you a flavour of what the book contains. It does not cover every single work of every major composers, and even when there is a mention, it can be very short. For example, this is what Mr Hinson has to say about a Rachmaninov prelude: "double-note study very difficult".
I suppose the book will be useful as a first port of call to look up some very basic information about an unfamiliar piece. It does not give much in-depth musical analysis.
I don't want to belittle the enormous amount of work that has gone into it. In this day and age, with access to resources like Wikipedia and Youtube, such a book has pretty much become obsolete and I'm afraid I don't see a new edition coming up.
Topic: Iberia Background