PIT meets my criteria for a 4 star airport for the following reasons:
1. Easy to get connections to major hub airports - ORD, DFW and IAH in particular.
2. Free wi-fi that isn't pitifully slow.
3. Great signage directing you to where you need to go.
4. On site car rental center.
5. Secret extra security checkpoint that is a breeze to get through.
Minuses:
1. Sub-standard airport lounge where you have to pay for your drinks.
2. Lack of non-chain food options.
P.S. Yes, the airport is showing it's age, but all things considered, I've been in much worse airports. They get a pass and the extra star for free wi-fi.