First of all, an observation area. If it were a really good one, with good, panoramic views, I wouldn't mind paying for it. Secondly, private security staff should be kept on a short leash (not literally, well . . . maybe) inside the departures area. That is to say, they should not be allowed to stop people from taking photos as is now the case in some airports. Thirdly, an aviation shop, with magazines etc. Fourthly, a good choice of food and restaurants.
Apart from that, I'm easily pleased!