Once they're in the terminal, travelers reported higher satisfaction when they found better amenities, more restaurants and a wider variety of stores and shops. In particular, Garlick has noticed a number of airports have added higher-end restaurants where travelers can sit down for a meal.
"This is a nice trend because airports are realizing travelers want more than fast-food options," he said.
On average, travelers who were most satisfied spent $29 while in the terminal at large airports, and $24 at medium-size airports. By comparison, those who said they were disappointed spent just $10 and $11, respectively, at large and medium airports.
According to J.D. Power, millennials registered higher satisfaction at airports than older travelers. They also spent the most money, with the average millennial who spent fewer than 50 minutes in the terminal shelling out $25. That compares to an average $18 for Gen X, $10 for boomers and $7 for "pre-boomers" who were born before 1946.
So, which airports received the highest ratings and which ones lagged?
Among large airports, Portland International in Oregon earned the highest score of 791.
"Portland does everything well," Garlick said. "It's very well managed and very efficient."
On the other end of the spectrum, Newark Liberty registered the lowest score, 646, which was well below the large airport average of 719. That's despite a recent upgrade to the airport's United Airlines terminal, which has won praise from travelers. However, congestion remains a major issue, which makes flights more prone to delays.