I've been playing the horn for coming on to seven years now and it still pulls me in like no other instrument I've ever played. There are things I can do on other instruments (piano, guitar, banjo, alto flute/flute, and cello) that I can't do on the horn, but none of them as consistently have me exploring how to make music.
Part of it is probably the fact that when I started the horn in my mid 50's, I already knew a lot about the generality of music making, which allows me to bring all that to bear in learning the horn.
Increasingly, though, I think it's the very tactile nature of playing the horn that has taken me so much deeper into the experience of music making. My hands, arms, and torso all vibrate in resonance with the tones I primarily feel in my embouchure. I love the feel of the resonance of the guitar/banjo, cello and flutes, but with the horn there's just more of it.
There's also more of a one to one relationship between breathing and phrasing than on the flute that I think has to do with all of the air going into the horn as opposed to being split by the embouchure plate and only some going into the flute.
For me the tone of the horn is simply larger and more malleable than that of other instruments, and somehow I feel more inside the tone experiencing it than being outside the tone and manipulating it.