I first sauntered into the Main Branch at 42nd St. as a casual tourist more than half a century ago. Little has changed since and the only bustling about seems to be from tourists wanting to take a peek at the Rose Reading Room...made famous in so many Hollywood movies. Nowadays you now need a reservation to even glimpse at it.
The "real" library, of course, is now to be found dispersed among many dozens of branches all up and down Manhattan and some more sprinkled around the Bronx. The most majestic branch, that would be the word, is the principal/largest circulating branch, The Stavros Niarchos Foundation Library (SNFL), just across the street from its parent. It is the most modern version of what a library should be for this new century. It's got books and much, much more. Libraries were never just about books, anyway: they were about making knowledge available to the masses. Well done New York.
I didn't have time to get over to the SNFL, it would have needed a day just for itself. There's a reason to go back to NY; to witness civilization at its best... as you might the Medici treasures of Rennaissance Florence.
There was a small library museum at 42nd St.... small but focused. Smart "curating". Among the displays a (the?) writing desk of Charles Dickens.
Interesting factoid: under Bryant Park, at the back side of the library, underground and just as extensive in dimension are hundreds of stacks of the library's holdings, including their giant research books collection. Remember, this was an important thing to even exist, no matter how large, before the world wide web.