I am sure the answer to that question varies from state to state, town to town, and person to person. It also depends on the perspective of the customer or the perspective of the restaurant owner. But, I'd like to outline the answer to this question in my own words based on my own experience as a customer, as a restaurant employee, and as a former manager of a quick service franchised restaurant (non-barbecue related by the way).
1. Above all else it must be clean. When you walk in to the restaurant is it inviting? Are the windows clean? Is the entry way uncluttered? Is the floor swept? Is the entry point easy to identify?
I'm continuously surprised and amazed at restaurants that fall short on most, or all of those basic considerations. If the glass door has hand prints all over it and it looks like it's not been cleaned in several days, can you imagine what the kitchen might look like?
2. How's the lighting? Some may disagree with me, but I like a lot of natural lighting. I know a lot of "fine dining" establishments like to keep the lights down, but I'd prefer they turn the lights up a little. I always wonder what the low light is trying to compensate for. And besides, if it's dark inside it's kind of hard to judge my first requirement (see #1).
3. How are the prices? I've paid $75 for a breakfast for two and I've paid $75 for a dinner for two, but I'd prefer to pay less. For a reasonable bbq dinner with meat and two sides, I'm comfortable paying $25 - $35. After all, are people likely to flock to a restaurant that charges $75 for dinner for two day in and day out? I'm sure there are exceptions - I can name a couple of non-bbq restaurants from own experience, but on the whole I doubt a lot of restaurants can stay in business long at $75. It kind of reminds me of that old business adage I hear from time to time: "I'd rather have 1% of the efforts of 100 people (i.e. $1-$3 from 200 - 300 customers per day) than 100% of my own efforts (i.e. $10-$12 from a few handfuls of customers per day).
4. How's the food? Is it mainstream? I like variations of simple foods like chicken, pork, beef, and fish. I'm not a cous-cous fan, nor am I a fan of small portion sizes of "foo, foo" foods. I took French language courses in high school and college, but I don't speak or read it fluently any longer...and I don't like French food.
5. How's the service? Are the waitstaff friendly? There's a steak place near Orlando that amazes me in this regard. We were there eating with friends and I ordered my steak medium-well. Understandably, some will say, "you don't go to a steak place and order anything more than medium", but I did and still do. When they brought out my steak, it was still bleeding on the plate. I mean it was actually pooling. The steak was closer to medium-rare than to medium even. I can eat medium, and often do, but I can't eat steak that's still mooing. How do you predict that the waiter acted when I asked them to cook it a little more? If you guessed that he said something along the lines of, "We don't cook steaks to medium well. At finer steak houses, the steaks are cooked to medium at most." Really? I didn't want to make a scene or anything, but the rest of my meal was less than enjoyable. And yes, they did accept my payment for the overpriced steak that I could barely choke down.
I could go on and on about my dining experiences. I enjoy eating out, and as you may have guessed...as a bbq cooking enthusiast and former restaurant employee for a variety of franchise quick service concepts...I also enjoy critiquing them.
And in case anyone is wondering, if I had a lot of extra money and the chance to open a restaurant I would gravitate toward a breakfast oriented diner concept. The profit margins are bigger and it's much easier to meet requirements #1 - #5. There's only one way to cook bacon and sausage :-)