90% of the time I order traditional duck (like the ducks they hang in windows or "Peking Duck") in a Chinese restaurant in NYC, I notice a very distinctive flavor or seasoning with a strong aftertaste.
I have trouble putting the flavor into words. It's somewhat soapy and complex and ever-so-slightly rancid, like meat that is very close to starting to turn. It's very strong and not subtle.
It's not just "the flavor that duck has". I've eaten duck at non-Chinese restaurants and made it at home, and it never tastes like that.
It's certainly not a pleasant flavor, but I wouldn't call it altogether unpleasant either. It's just... strange. Ultimately, I prefer the preparations of duck (Chinese and otherwise) that don't have this flavor. Mostly, I'm just curious to know the source of this flavor.