Actually the Biltmore was demolished and replaced by a totally nondescript box. You are thinking of the equally fine Commodore Hotel (though not as good internally) It became the Hyatt Hotel and is as you say completly unrecognizable and completly forgetable!! I think the loss of the Astor was a terrible blow to the Times Sq. area, all the great theatres are also gone so the place is just a memory now trading on it's name but totally rebuilt from it's golden age of the 20's to the 50's.I actually agree with you... for once.
The Gillender Building is probably one of the best examples considering its short lifespan and how it makes 14 Wall Street look boring.
Anyways, some NYC buildings.
City Hall Post Office and Courthouse:
Madison Square Garden (original):
Biltmore Hotel (still existing, but completely unrecognizable):