Franz Liszt was a man who found his gimmick. There were other piano prodigies before him, like Hummel and Liszt's teacher Czerny, but none created the frenzy that followed Liszt in his youth. In 1847, toward the end of the period covered in The Romantic Generation, he stopped touring and settled down to a regular job in Weimar.
And what was his gimmick? He could take common popular pieces of the era, such as operas, and decorate and transform them with dazzling, almost impossible ornamentation. This was his wow factor. You can imagine the audiences going mad over this. This gimmick required him to dazzle while continuing to remind the audience of the original material. He was more fabulous than three tenors all in one.
In the Transcendental Etudes he applied this fabulous ornamentation technique, a technique that was based entirely in the art of improvisation, to his own youthful etude compositions. He could do it with anything any time he wanted. Eventually he could not resist it and applied it to everything his eyes fell on. Occasionally he would write one of his improvisations down and call it a composition. He was completely undeterred by crassness or bad taste.
Charles Rosen does not manage to say anything this straight forward. He is a pianist and writes like a pianist talks. I remember them. They were the only people who sat during their coffee breaks and obsessed over the minutia of piano technique. I have in all my life never heard two singers get together and do this. Except maybe tenors talking about their cover technique.
When played by a pianist of sufficient technique, it is fun to listen to Liszt's piano pieces. I have personally never heard such a pianist. Usually you feel that it would be fun if only.... It would have been interesting to hear Rachmaninov play Liszt. [My friend Jean says that indeed, it was.]
Rosen is trying to assess Liszt in the way he would (and does) assess Chopin and cannot. Liszt did not have the fabulous originality and compositional creativity of Chopin, but Liszt had something else that I wish Rosen would talk a lot more about. Liszt is the creator of the orchestral tone poem, the bridge to Wagner.
Liszt is monumental for his influence, for his desire to create large forms only tenuously related to the sonata form, for his success in tweaking the imagination of another more gifted in actually composing.