I have heard almost nothing by d'Indy; in fact, it's quite likely that the work featured in this post is the only work I've ever heard by d'Indy. My brief research confirms that his music is little heard today outside of the present piece, although in his Essential Canon of Classical Music, David Dubal does opine that d'Indy is a terribly underrated composer, so perhaps his work is deserving of greater exposure.
This work, the Symphony on a French Mountain Air, is unusual in a number of ways. First, it is in three movements instead of the traditional four; second, its melodic material is mostly derived from a single tune (the "mountain air" of the title, a song d'Indy heard while traveling in the mountains); and third, the work features a prominent (but not quite dominant) part for a solo piano, making it a sort of symphony-concerto hybrid, not unlike Harold in Italy, the symphony by d'Indy's fellow Frenchman Hector Berlioz, which had featured a prominent part for solo viola.
The Symphony on a French Mountain Air is, to my ears, a delightful listen that always feels fresh and light, especially after a steady diet of heavy Germanic romanticism.
Next week: Well, I haven't decided yet, but there is a big-name Russian composer knocking on the door....