PIT ended up solidly above average (among medium airports) in the latest JD Power customer satisfaction survey:
http://www.jdpower.com/press-releases/2015-north-america-airport-satisfaction-study
I've been flying a bit more recently, and a couple things stand out to me about PIT.
On the negative side, contemporary airports have gone to soaring terminals with lots of light, and PIT by contrast seems cramped and dark. Unfortunately, new floor treatments and such can only help a little (although the central core retail area specifically did benefit a lot from the refresh and new floor). So you'd basically need a whole new airport to truly fix this--and we are still paying for this one.
On the positive side, PIT remains an extremely easy airport to get around. The one-stop shuttle with the four terminals radiating out from a central core remains a very convenient approach, and the alternative security point has really helped.
Bottom line is I think we will have to live with "not the nicest but quite convenient for travelers" for a long time to come, which ultimately is proving sufficient as indicated by this survey.