This 4000-page "Nueva gramática de la lengua española" is a real goldmine of knowledge. It is surely the best systematic grammar book I have seen for any language. There are 11 chapters on morphology and 37 chapters on syntax. The style of writing is in itself educational to read. Each chapter is organised into sections which are organised into paragraphs which are semi-self-contained mini-essays on detailed aspects of the language. Each sentence in these paragraphs seems to be written with a view to being a model of good grammar and expression, and each paragraph is well-structured. It's a delight to read.
I bought this book and the much smaller (305 pages) Nueva gramática básica de la lengua española (which is condensed from the full grammar) at the same time. At first, the size of the full grammar book seemed so great that I thought it would gather dust until I was advanced enough to use it. However, the first thing I looked up in the concise version (concerning conditional constructions) was inadequately covered in a 7-page chapter. So I took a deep breath and waded into the corresponding 104-page chapter in the 4000-page work. Result: Pure pleasure! This book systematically presents a very wide range of conditional sentence structures, with multiple variations, giving explanations for when and how to use each kind of construction, contrasting the subtle differences in meaning between similar sentence structures (which are distinguished by mode and tense in particular). Numerous useful examples are given for most points. Judicious use of underlining draws the eye to the relevant parts of example sentences. Fonts and typefaces are used effectively to facilitate comprehension. Adequate and useful cross-references are given to other parts of the book.
I have several other Spanish grammar books, and they are all unsatisfying because they leave out so much detail that one cannot fill in the gaps. With concise grammar books, one has to try guessing phrases in a search engine to assist the discovery of correct grammar from online examples. The comprehensive RAE grammar book makes such desperate searches on the internet redundant.
One of the things I particularly like about this grammar book is the analytic order of presentation. By this I mean that the presentation starts with smaller units of sentences and builds up to multi-clause sentence structuring. Thus the first 11 syntax chapters (chapters 12-22) are about nouns and nounal phrases, adjectives and adjectival phrases, definite articles, indefinite articles, personal pronouns, demonstratives, possessives, quantifiers, numerals, and relative/interrogative/exclamatory connectives. This is all before verbs are discussed in 6 chapters (chapters 23-28). Then come 4 chapters on prepositions and prepositional phrases, adverbs and adverbial phrases, conjunctions, and interjections and interjection phrases. Then there are 16 chapters on all aspects of sentence construction. Some people prefer to start with whole sentences and then fill in the details. For this purpose one can start by reading the later chapters and come back to the details later. But in my opinion, the systematic synthesis of grammar from low-level word groups up to multi-clause sentences is the best approach for a truly comprehensive grammar book such as this is. I wish I had such grammar books for other languages!
I have only briefly mentioned the initial 11 chapters on morphology because most medium-size grammar books do a fairly satisfactory job in this department. However, this grammar book gives the same thorough, comprehensive treatment to morphology that it does to syntax, which goes far beyond what the concise grammar books give. By contrast with the syntax sections, the morphology sections have a large amount of information about variations between countries. Just as one example, paragraph 6.12f discusses national and regional variants of nouns using the suffix "-ería", such as the word "pupusería" (a certain kind of tortilla), in 10 countries. This country-by-country treatment is seen repeatedly in this chapter about noun suffixes. Chapter 7 has the same level of detail about adjective and adverb suffixes. Chapter 8 covers similar variations of verbs.
All in all, this is a real feast of grammar. If a grammar book has a little "too much information", you can be selective and dip in where you wish. But a grammar book with too little information is useless if the detail which you want is not there.
This grammar book is also pure pleasure to own. It's nicely printed and bound. It is structured admirably. And the prose is clear and elegant. It is more expensive than the average grammar book, but I expect to derive a lifetime of satisfaction from these two weighty volumes.