Philadelphia to most is not a great city. However once in Phlly many never turn back. The native Philadelphians rarely leave and defend their city with all of their energy.
I, myself am a convert from New York. Philadelphia initially wasn't so great from my perspective but there's a lot to see and do. There's been tremendous improvement over the last decade.
Philly has some of the best eats around. There is always a new opening of a restaurant and the variety is really great. You can always find something unique regardless of the neighborhood you're in.
The other thing about Philadelphia is that it's a city of neighborhoods with distinct cultures and offerings for the city. The Center City is the CBD and just outside of Center City is University City where many colleges are. Philadelphia is another college town (after Boston). While the concentration is very much in University City there are a myriad of post high school institutions that span the city's borders.
Now Philadelphia is in change. A new Mayor, new buildings, 'renovation' of the city.