Cycling in NYC is highly dependent on the bike lanes on your route. There are good stretches of quality bike lane here and there (especially in Brooklyn), however there are parts of e.g. Chinatown that I would not recommend on a bike.
I would add to that list the entirety of Queens, where I regularly see people cycling down Northern Boulevard. I'm not familiar with roads in other cities to compare it to, so you'll have to use your imagination when I say: it's very dangerous.