I've read some airport-related planning literature about the interiors of airports and about their public transit connections. (For a good example of the latter, see http://www.planetizen.com/node/34842 ) But one other difference between airports relates to their exteriors: the difference between walkable airports and not-so-walkable airports.
Many airports resemble that of Jacksonville, Florida (where I lived until a week ago). The airport is 15 miles or so from downtown Jacksonville, and is along a long stretch of vacant, undeveloped land. If you were to walk outside the airport, you would be utterly disoriented: you wouldn't know whether you were in a big city or a small town. So as a practical matter, the only sane way to exit the airport is by car or bus.
By contrast, a few nights ago I arrived at the airport in Little Rock, Arkansas. As soon as I left the airport terminal, I could actually see the towers of downtown Little Rock. More usefully still, I could see the hotel I was staying at, and (after a minute of false starts) was actually able to walk to it. The airport was hardly in an urban environment: I walked on grass instead of on a sidewalk. Even so, I felt like I was near a city, rather than in the middle of nowhere.
Better still is Providence's airport, where a decade ago I was able to walk from the airport to a thriving inner suburban neighborhood. I went on walkscore.com and was not surprised by the results: the Walkscore of Jacksonville's airport address was 15 (primarily due to on-premises shopping), the Walkscore of Little Rock's airport was 22, and the Walkscore of Providence's a stunning 65.
Of course, an airport cannot be as walkable as, say, a bus or train station: often, an airport needs to have spare land so it can expand in the future. Nevertheless, an airport that is near other visible amenities, like a train station near such amenities, is inherently a more pleasurable one.