The 90's version of NY-2 and NY-3 were a bit closer demographically, though NY-2 has always had a higher minority population. The pro-incumbent gerrymander of the last redistricting changed it a bit. Notice how the lines of the Suffolk portion of NY-3 bounce around a bit. The Suffolk County portion of NY-3 tends to be very Republican, mostly middle class and a relatively small Jewish population. Especially look how the lines are drawn around Amityville/North Amityville, Copaigue and Bayshore.
I've been to Brentwood in recent years and seen how diverse it has become. There are families from all over South America. I don't know if its just there or other places in Western Suffolk. It seems strange that on Long Island the outer suburbs have a higher minority population than the inner ones (although there are Elmont and Hempstead so its not completely true).
The border between NY-2/ and NY-3 in these areas tend to separate heavily African American or Hispanic neighborhoods (on the NY-2 side of the line) from the mostly white neighborhoods (on the NY-3 side). Many of the portions of Suffolk in NY-3, especially southern Copiage, Lindenhurst and southern Bayshore are heavily Italian. The south shore of Nassau County (especially the Massapequa area, and into Farmingdale are heavily Italian (North Massapequa is just about 50% Italian)
Also take a look at the areas in eastern Nassau where NY-2 cuts into. This doesn't play the racial bouncing around game the Suffolk portion does, but the NY-2 portion of Nassau generally covers upper middle class heavily Jewish neighborhoods (Woodbury, Jericho, Syosset, Plainview)
I've found the northern half of Nassau to be much less dense, with more trees and bigger lots, than the south shore. Parts are very wealthy and full of country clubs, like an inner version of the Hamptons. I didn't know those areas were more Jewish than other areas of LI.