It's not complete, but it has all the stuff you need to hear. I just finished CD 10, which is chamber music. All the remaining discs, except for one bonus disc of oddments, are vocal music: seven CDs of songs, the opera Pelléas et Mélisande and some choral music. I might have something to say about this surprisingly large quantity of vocal music afterwards, but for now, let me just say a couple of things about the first ten discs that contain most of the music that is well-known.
When I was a young listener I instinctively sought out the most esoteric kinds of music--as soon as I realized there was such a thing. I would read books on music that mentioned the wilder fringes of the avant-garde, or eccentrics like Gesualdo or Harry Partch and I would seek out their music. I suppose this aesthetic principle, which was never expressed consciously at the time, might be worded as "the greater aesthetic truth lies in the music that is the most out of the ordinary." There is a grain of truth there, of course, as the most common denominator music is probably not the highest quality.
But years later I ran into the writings of Donald Francis Tovey, the great English musicologist, who talked about the idea of "normality" in music. He used this idea to talk about the elemental nature of some of the music of Beethoven. And I also started to get an idea about the Classical style and how it gives us a kind of aesthetic standard. So slowly it dawned on me that probably the most important music, aesthetically, was not out there on the fringe somewhere, but central to music history. The quartets and symphonies of Haydn, the concertos and operas of Mozart, the piano sonatas, quartets and symphonies of Beethoven: this is where the real meat is.
Getting back to Debussy and setting aside the vocal music for the present, the "meat" of Debussy seems to lie with the piano music as that is where a lot of his energy was focused. Of the ten CDs of instrumental music six are devoted to the piano. The remaining four discs consist of three discs of orchestral music and one (1) disc of chamber music! This, combined with the fact that the box contains four discs of songs for voice and piano, points to the realization that Debussy is a composer who comes out of and is based in the salon. Here is a photo of Debussy in 1893, at the piano:
The songs for voice and piano and the solo and duo piano music were the bulk of his work as a composer. Added together they come to ten out of the eighteen discs. The surprising thing is that only ONE disc is devoted to what we usually think of as chamber music. This disc contains the early string quartet, the sonatas for violin and piano and cello and piano, the trio for flute viola and piano and the flute solo Syrinx. That's it, that's all the chamber music he wrote excluding the music for piano and voice and piano. I suspect that Haydn or Mozart might have written more chamber music than this in the course of a single weekend! One string quartet? My box of Haydn string quartets has 21 discs. Obviously the string quartet was either really unimportant in turn of the century France, or Debussy was a very bad string quartet composer. I have to say that it is not a particularly impressive piece. But it remains an interesting fact that Debussy wrote many, many songs, but almost no chamber music.
The classical song seems to have become important in Vienna in the late 18th century. There are hosts of lieder (German for "songs") by many composers and superlative examples by Schubert and later Schumann. This tradition continued in Paris in the late 19th and early 20th centuries. But it seems to have fallen on hard times lately. None of the chamber music series I am personally familiar with hires singers to do song recitals. But they hire a lot of string quartets. Of course the music world generally is dominated by popular song and a very large part of the classical musical world revolves around opera, but the classical song recital is just not very popular these days. I wonder if we could see a revival sometime soon?
Hauling this discussion back to what it is supposed to be about, the "normal" for Debussy in instrumental music is the music for solo piano and this repertoire is full of fascinating pieces both innovative and charming. Second to this are the equally colorful pieces for orchestra. The chamber music is, for Debussy, a fringe medium, so don't expect too much. Perhaps the most central of the central work of Debussy are the preludes for piano in two books of twelve pieces each. Let's have a listen. Here is Krystian Zimerman with all 24: