At its peak it consisted of 5 lines serving 33 stations between 4 terminals, the parking lots, a hotel, and a number of stations for airport employees.
That's bigger than the transit systems of many cities.
But it wasn't that convenient by modern standards. The trains were slow, only moved in one direction, and 4 of the 5 lines were located outside security.
Despite being a bit smaller, Skylink is still the largest airport people mover system in operation today.