I go frequently because every day, from 2-4pm, 44 oz. strawberry limeades are on "happy hour". But more importantly, chunks of more or less real strawberries come up the straw into your mouth. There are also real limes down in your gargantuan tankard of ice crunch and sweet sweet nectar. For a dollar.
Sometimes I get something big and fried at Sonic and it makes me feel a little gross, but on the whole their food is great if you can handle its intensity of flavor. I should note that I have a very fond memory of eating bacon cheeseburgers (and the aforementioned strawberry limeades) there after a hard day's work, but that could have been the heat and poverty of the Tennessee county in which I was day laboring, or my avid youth, or the sheer novelty of my new southern surroundings. I do stick more to drinks and desserts if I go here though.
Total Americana - there's a lot of junk to pick through, but you can make your personal choice for something special. I chose limeade.