When one thinks about drive-ins, one can't help think of George Lucas' American Graffitti or Happy Days. It's this type of ambience that the Sonic franchise is hoping to capture in each of it's drive ins.
That having been said, I don't remember a drive-in restaurant from my youth (except a drive-in theater, and that was in Atlanta). There is a kitchen building where the wait staff roll (or walk if they haven't purchased their own skates) to pick up the food to be delivered to...the customer's cars! The parking lot is centered around this building (like a doughnut). At each parking space is an electronic menu board - press the button and speak your order into a speaker/microphone and, magically, someone appears with your order on a tray. You can enjoy your cheeseburger with chilli-cheese fries and Coke in your trusty Ford or Chevy, listening to your own music (or roll down the windows and listen to Sonic's canned 50's-Today music - or your neighbor's parked next to you, if it's turned up loud enough).
Dont' want to eat in the car? Don't worry. There are benches next to a volleyball court, children's playground and a batter's cage. If it's hot, there are fans on the covered area around the benches to help cool you. If it's cold, well, wear a hat and coat!
Overall, it's a pleasantly unique experience. I don't like to eat in my car - I've done it enough over my lifetime that it's more of a punishment than novelty. The kids like it because of the play area and the cool way they get to place their food order. And they like the food - and so do I!
Oh, and did I mention the treats? Sonic has some of the coolest desserts and treats in the fast food rhelm. That is why I use Sonic as a treat whenever someone cleans their room without being asked or has a nice grade to show off on the refrigerator.