Location is fantastic for seeing the sites, restaurants and nightlife. The apartment is very clean, spare and spacious and (at least for our purposes) is very comfortable and user friendly. We're in Philly a couple of times a year and plan on renting this apartment again. Definitely recommended.
The one flight up is quick and easy even with luggage and bags of food.
The only reason I didn't give it a five is that it can get a bit noisy at night being smack in the center of town... We were so tired from the day that it didn't make a difference.