Markus--
I really enjoyed this!
You mention Onslow-- I love his chamber music. As Henry mentions, this is more Mozartian/Classical than I would identify with Onslow (certainly mature Onslow). That said, it is a solid piece.
A few comments:
The intro is almost Baroque in its tone, and seems a real mismatch for what follows. A "custom" opening might serve this piece well. Anticipating my next comment---a more chordal/fanfare/block chord kind of treatment might offset and highlight what follows well by means of contrast--avoiding DBC--"Death by Counterpoint".
which brings up...
Contrast. One of the reasons I really love the romantic period idiom is the flexibility and expanded expressiveness---while integrating counterpoint, classical phrasing. Your piece stands on its own, but perhaps there is room for more contrast with the counterpoint? WWOD? ("What would Onslow Do?"--its a thing now with the kids...). That said--your counterpoint is wonderful!
Bar 40.: missed opportunity with the Bassoon? It just struck me that a moving bassline with 3rds might serve well here and really make this section pop. Anyhow, it is out of character with your writing for the rest of the piece.
The piece deserves more of my attention, but these are things that struck me, right or wrong. Overall a great piece of music!! I'm currently flubbing my opportunities for counterpoint in my PQ---I keep saying "In the development! In the development!..." We shall see. Yet again you set a very, very high bar!
Thanks for posting!