Okay so 16 views and no replys so I'll just go ahead then.
Intelligence: Washington during the siege of Boston had accurate and steady flow of intelligence on the situation of the British in Boston (numbers of effectives, supply situation). At New York the situation was completely reversed, Washington had no reliable intelligence regarding the disposition or health of the British on Staten Island or Long Island.
Consequently Washington seriously underestimated the strength of the British forces on Long Island(he thought 15,000-20,000 in reality it was over 20,000) and overestimated the threat the British reserve on Staten Island posed to New York(he believed 10,000-15,000 remained in actuality it was only about 2,000). The main reason for this disparity is again Washington did not have accurate intelligence on the number of effectives(over 10,000 were sick due to various camp illnesses).