The Chicago fair opened after most of the pre-Depression Art Deco and Moderne office towers had come on line and little was being built. To a considerable degree the thrust of the trend towards architectural modernism had been halted. Its evolution had effectively ceased aside from doodles in architects' sketchbooks. The New York fair came later in the architectural drought at a time when the Depression was easing, but few large buildings aside from government structures were being built. At least it created an opportunity to look ahead while entertaining fair attendees.
By the early 1960s when the 1964-1965 fair was being planned, the "future" that the '39 fair attempted to predict had already happened in the form of a modernistic building boom in New York City and elsewhere. Rather than featuring Progress or The Future, this fair's weak theme was "Peace Through Understanding." As best I could tell, it was virtually invisible to fairgoers, there being no pavilions from major nations due to the fair's lack of BIE sanctioning.
Nevertheless, the fair's architects and designers did their best to show off, and a number of pavilions were future-oriented in what was on display. So the fair's architecture ranged from attempts at showing the future to whimsical structures to even traditional or historical recreations.
The fair was not a great success. And it did not excite me when I visited it in June of 1965 during the second and last year of its run. Information regarding it can be found here.
Below are some photos I took.
Unisphere. A giant cliché that might well have been selected by an unimaginative committee. It still exists.