The other book I was given for Christmas is Alec Ross, The Rest is Noise
This examination of 20th century music is a masterful look across the whole century relating the music and how composers came to it with the social, political and economic circumstances.
It's a book to dip into rather than read at one sitting. And it's one of those books that cause you to go listen to the music, more informed than before.
To accompany the book there is a website where you can find articles, audio clips of music and countless other excitements. Reading an entry in the book led me to the website where I found a clip of the music of Morton Feldman, which has now resulted in me buying more of his music.
This is the best kind of book that opens up a door to you.