Frankfurt is a great town....
But bring your own sticks... prices are seriously HIGH in Germany by comparison with what you can purchase stuff for in places like Dubai, Turkey, etc..
If you have some time to play tourist, get outside of Frankfurt.. hop a train to Wiesbaden (suburb on the outskirts of Frankfurt.. about a 20 minute train ride from the center of the city IIRC).. and check out the hot springs/spa (one of the oldest in Europe I believe..)..
There are lots of museums, and some decent old archetecture (old cathedrals, etc..) around Frankfurt if thats your sort of thing.. but its not really a very touristy city..
If you have a day free.. consider hoping the train to Strasbourg, France.. its about a 2 hour ride.. but WELL WORTH IT... Great town.. awesome food/restaurants.. great old gothic structures everywhere.. etc...
If you havent flown into Frankfurt before.. its a HUGE airport.. one of the largest, and busiest in Europe.. but, like all things German, its extremely efficient.. and very easy to navigate.. the United/Star Alliance lounge is one of the better Star Alliance lounges in Europe (IMO).. and if youre looking for a place to crash, there is a decent Sheraton inside the airport to grab a room at (although a little expensive)..