This is by far the best airport diner in the Northwest. As a pilot I've eaten at most of the airport (and near airport) restaurants and this is my favorite. I have never had a bad meal over a decade of eating here. The food is very reasonably priced and is always good. It's true that they can get busy and you might wait a few minutes for your meal. Would you rather eat somewhere the food was lousy but you got it right away? Not me.
Their portions are huge. My wife and I usually get there about brunch time and our breakfast or lunch is usually our only meal for the day! Inexpensive meals and huge portion sizes is not my criteria for a good restaurant. Quality food is the only thing, and the Airport Diner delivers.
You get to watch airplanes taxi up and park a few feet from your table and half the fun of eating there is just watching the planes taking off and landing. The breakfasts are great and their lunches are too. I have not had the pleasure of eating dinner there yet but I wouldn't be surprised if they weren't just as good. Give them a try!