a current student here
1) Decide if you are more interested in technology or pure science. Poly is a fantastic incubator and collaboration center for technological and engineering endeavors; however, it is a poor substitute for a college of arts and sciences if you have a more theoretical or research interest in science.
2) Poly is a small school in a big city. New York City is one of the most incredible places I have ever experienced. Restaurants, clubs, parks, historical landmarks, beautiful Central Park, magnificent skyscrapers--the city environment is incredible. Poly is a pretty small school for those who enjoy the tighter community; however the expanded community of all the NYU schools is right at your disposal for those who wish to experience it, thus giving you pretty much the best of both worlds (small and large schools).
3) Calculate expenses. Poly is an expensive school so make sure you figure out your expenses before you reject your backup school. The financial aid and admissions officers are definitely on your side though, and they are pretty generous with their financial and merit aid. When I was accepted, I talked to them until I was able to get an extra $2000 grant from them to cover the rest of my tuition.