The big deal with a lot of chain restaurants (like Cracker Barrel and Denny's, plus truck stops, for instance) is that they buy their food in a can or box and just heat it up. I greatly prefer real home-cooked food, but that is REALLY tough to find on the road.
As to genre of food, I like all sorts of different dishes. Recently we've been trying out some Middle Eastern fare, and it is some REAL good food. Tabbouleh (bulgar wheat, green onions, parsley, garlic, lemon, seasonings), smoked and fire-grilled skewers, meat of your choice, w/veggies, and a few of their other dishes are worth finding. We're making a big bowl full of Tabbouleh right now for supper. If you are ever in the Louisville area, check out Shiraz Mediterranean Grill. Worth however long it takes to get there! http://www.shirazmg.com/menu.htm
We're also really fond of BD's Mongolian Grill. There, you take a good-sized bowl, fill it with whatever turns you on (steak and potatoes if that's what you like!), anything from shrimp to fish to steak to vegetarian choices, top it with vegetables, add a sauce and seasonings (everything from bar-b-que sauce to hot and spicy oriental) and they grill it right in front of you. REALLY good meal, and a fun place to try. The flavor and type of food is whatever you decide to stick in your bowl. http://www.gomongo.com/
We stopped at Lambert's Cafe -- "Home of the Throwed Rolls" on our way back from Missouri. What a fun place. Good food, and PLENTY. Whatever you order from the menu will be enough to feed you for another meal at least, then they walk around with extra side orders that they just scoop onto your plate (no extra charge). Want a dinner roll? Hold up your hand and get ready. They'll toss one from across the room. ;D I'd stop there again in a heartbeat. http://www.throwedrolls.com/shopcontent.asp?type=Tour
I've sort of fallen out of love with Cracker Barrel. We tend to search out Mom and Pop places instead. They're still around, but take some searching. The new apps on smart phones help in that regard. Other places, like Mc.D's are off entirely unless that is the only choice. I'm having a hard time finding actual food in some of those sort of places... Mc.D's advertises that all of its beef is 100% pure. Of course it is, but that isn't the only ingredient in a patty... :
Arbys -- ever (ever) cook roast beef that didn't have a lick of gristle in it once in a while? Leads me to believe that there is no real meat involved in their roast beef sandwiches.
Anyway, the best meals are when we pull up to a camp site and get the fire started. Hard to beat that! ;D