It's hard to assess Hiller since so little of his mature work is available. He was initially weak in precisely those areas where Mendelssohn was strongest, but he took Mendelssohn's criticisms to heart, especially after he stopped hoping for success in opera, and subsequently reinvented the concerto form with his second piano concerto, which, unlike Chopin's (or his own) of a decade earlier, eschews the successful but now predictable conventions of Field and Kalkbrenner. Mendelssohn and Liszt were working in the same direction, of course, but it was Hiller's new model that Schumann adopted, and later all of the Schumann imitators, such as Grieg. It's also evident that by the time of Mendelssohn's death, Hiller could write an internally coherent Durchführung with the best of them. In achieving the mastery evident in the few late scores of his that are readily available, Hiller sublimated his passion a bit more than Mendelssohn needed to, and this I believe has contributed to Hiller's unsung status. He did, however, have his own voice. And he pushed both himself and the musical culture of the communities where he worked very hard in the direction of high artistic ideals. It is because of musicians like him that the last third of the 19th century produced so much extraordinary music, perhaps the best overall that Western Culture has seen so far.
Nothing in Hiller can match the sublime slow movement of Berger's Piano Sonata, Berger's stunning fugues, many of Berger's chamber works, or Berger's second symphony (the content of his first being unknown to me). But then few musicians have produced so much music that was both spiritually deep and technically accomplished.
Since joining this forum, my experience with D'Indy has been twofold: I have found new things to like in works I've known most of my adult life (like the first symphony) and many new pieces (such as Rivages) that strike me as being of the first water.
