This is what I've always thought of as "brassy" (in a bad way) ..... The beginning trumpet player's brassy splattering. I think maybe we all went through that period as beginners.
But "brassy" (in a good way) to me means that it has life and sizzle and edge to it ...... It's a TRUMPET for G's sake ..... It's not a flute, it's not supposed to be mellow (unless the piece calls for it). That "brassiness" is the EXCITEMENT in the instrument.