The Americans had made a daring and superbly executed move.

From 1776 by David McCulough. Page 191. 

Friday, August 30th. In the morning, to our great astonishment, found they had evacuated all their works on Brookland…with not a shot being fired at them…neither could our shipping get up for want of wind, and the whole escaped…to New York.

The immediate reaction of the British was, as Major Stephen Kemble recorded in his diary, one of utter astonishment. That the rebel army had silently vanished in the night under their very noses was almost inconceivable. The surprise for the British was no less than it had been the morning of March 5, at Boston, when they awakened to see the guns of Ticonderoga on Dorchester Heights. The great difference now was a feeling of relief, not dread. All at once the whole of Brooklyn and its elaborate defenses were theirs for the taking and the rebels were on the run.    

[snip]

As for the rebels and their flight, Serle, like many of the British, thought they had “behaved very ill as men.”

But there were those, including General Grant, who saw that the Americans had made a daring and superbly executed move. They had “wisely” gotten out when they did, General Clinton would later comment, and “very ably effected the retreat of their whole army.” Charles Stedman, an officer under Lord Percy, would later write a widely respected history of the war—one of the few histories by someone who was actually in the war—in which he called the retreat “particularly glorious to the Americans.” Further, he saw, as apparently Grant did not, the peril the Americans would have faced in the event of a change in the wind. Had the Phoenix and the Rose, with their combined 72 guns, fetched up into the East River as they had done before on the Hudson, Stedman emphasized, any chance of escape would have been cut off “most completely.”