I wouldn't say it's true for every major city in US, but yes, unfortunately NYC is decaying. NYC is mess you can't compare to Boston or, let's say, Chicago. Current infrastructure is already stretched very thin, but that's one thing, corrupt and incompetent local government deserves it's own story. If residents don't get their shit together and start voting for the change, it will all end badly.
I wasn't trained in smelling, but I definitely agree New York is a smelly city. That's one of my biggest memories how smelly it was.
Berlin can be quite smelly, too. Not every big city is smelly though.
I haven’t lived in any other large cities in the United States (only a handful in Australia), but is this a common experience for people living in other large, dirty cities or am I just being overly dramatic?