Purdue is ranked higher but by just one spot or so. The overall ranking is kinda meaningless though for engineering school. You want to check out if the department you are interested is strong. Fortunately most disciplines are pretty strong at NU. The ones that are strongest and are in the top-10 are material science, industrial engineering, civil engineering and mechanical engineering. ChemE and BioM are also very strong too (like top-15). EE and CompE seem to be less heard of but they are actually still ranked around 15-20. So I guess pretty much all programs are in the top 20.
There's no financial engineering MAJOR at NU. But "industrial engineering & management science" department does offer classes like stats, stochastic models, accounting/finance, and financial engineering. It's the closest thing to FE you can take at NU and along with econ, you will be in pretty good position to get into grad school for financial engineering or head straight to the Wall Street. You may also want to check out MMSS (mathematical methods for social science) program--good program for those interested in math and econ/social sciences. NU is definitely one of the schools that have a lot to offer for aspiring "quants" in biz/finance.