Frankfurt has a rep as the most "american" city in Germany. It´s the finance headquarter of Germany, but also the city with the highest crime rate, it depends on where exactly you want to spend your time. You should be safe in the inner city districts, but I wouldn´t suggest the surrounding suburbs. It´s in the state of Hesse, which is famous for their "Eppelwoi" (Applewine). There aren´t many culinary specialties I could suggest, aside from the typical sausages.
To be honest, Frankfurt wouldn´t be my first choice as a tourist, it´s a rather ordinary city. If you´ve got some time to spend, I suggest you visit some of the more rural areas of Hesse, as the landscape is quite beautiful there.