Music Composers Unite!
I really like it, Ario. The dynamics and the contrast between quick movement and pauses will work excellently if the performers are accomplished.
(In my opinion that's the best thing about 12 tone stuff - the latent drama. A lot of people outright dislike it, but even now this sort of music is used for its atmospheric invocations in film, tv and elsewhere, like it or not).
But I haven't got time to analyse your serial technique. As you'd know, that's quite a time-consuming task :) The one thing maybe to remember next time is that the horn can be dramatic in it's very low range: anywhere up to 2 (yes 2!) octaves below it's written middle C (obviously the lower you go the more extreme a technique it becomes).