I played the french horn for about seven years as a kid. I was second chair all-city in the Milwaukee school system in 8th grade but shortly afterwards got braces on my teeth. Bleeding gums were a major disincentive to practice and I guess I found cooler things to do. But I still love the sound of the instrument.
There are lots of great horn parts in classical music although unfortunately there's not a wealth of concertos that feature horn soloists. Mozart wrote four horn concertos that are probably the most performed compositions for horn. One problem is pieces up to the mid 19th century were written for and performed on the natural (valveless) horn which limited the palette for the composer.
Valved instruments opened up new chromatic possibilities on the horn. Richard Strauss wrote two horn concertos that are worth a listen. His countryman Paul Hindemith composed a horn concerto specially for the British horn virtuoso Dennis Brain in the 1950s. Sixty years after Brain's death in a car accident at age 36, he remains the most famous master of the instrument. He lived in the era of radio and LP records so his exquisite pure tone can still be heard in glorious mono.
Richard Strauss - Horn Concerto No. 1 Op. 11 (Dennis Brain)
Felix Kleiser is a 28 year old German musician who was born without arms. He plays the instrument using his left foot. It's quite remarkable to watch his toes move on the valve levers. Kleiser is unable to use hand-stopping, one of the traditional techniques of changing the position of the player's hand in the horn's bell to dampen the sound.
WA Mozart - Horn Concerto No.1 KV 412 (Felix Kleiser)