The 5 stars are for visiting the Cathedral as a tourist. I've brought two friends from Memphis to visit Pittsburgh on separate occasions. Each time, I thought I'd just point out the Cathedral since I'm a Pitt alumna and it's pretty and I had classes in there blah blah. Each time, the friend wanted to look inside...And suddenly we're paying the $3 to take the tour of the Nationality Rooms. And they LOVED it. I was a little shocked by how much out-of-towners loved this building and the audio tour, but they did. Even my parents and grandma--all locals--insisted upon a mini-tour when I graduated. The first thing all tourists say upon entering is "it looks like Hogwarts!" The Gothic architecture is gorgeous, and details put into the rooms are stunning. If you can, take a guided tour to see the Early American Room, which has a secret staircase leading to a secret room and supposedly is haunted.
Tourtists: Go up to the Honors College on the 35/36 floors for panoramic views of the city. These are the highest floors common folk are allowed to go to, though there are 42 floors total.
As a note to be totally fair: As a student, I'd give the building 3-stars. The elevators are pretty fast--if you can get one. Because most people are unwilling to walk up a few flights, I regularly waited 10-15 minutes to catch a car to the 30th floor and above. The Nationality Rooms are incredibly beautiful; however, many of these rooms have seats, but no desktops. Or the seats are benches. Not practical for holding a class. There is an absolutely no food or drink policy, and a 3-hour class without water can be as painful as sitting in a backless chair for that long. I only had one professor who loved being in the Hungarian Room so much that he incorporated nonsensical Hungarian themes into his lectures. Every other time, the professor put in a room change request and we moved a regular room.