I have always maintained that ppl in NYC are super friendly and open, I made great friends that I will cherish forever. Its a melting pot of cultures and everyone feels welcomed because of it.
If by NYC you mean Manhattan+The Bronx then I'd have doubts about the friendliness. Wall Street, after all, is one of the least friendly places on this planet. Dog eat dog. The Bronx... it changed a bit, most of the unfriendly people have been pushed north, towards Yonkers and such. Still, The Bronx is not what comes to mind when one thinks about "friendly".
If you look at other boroughs then the friendliness varies too. From Russian mob in Brighton beach, to Astoria where it was hard to rent a place if you weren't Greek or Italian.
A melting pot it is though, but I could never decide whether that in fact was good or bad.