About the joint
The Five Guys Burgers & Fries story is a rare tale. They went from a mom & pop greasy burg takeout only joint to a 2000+ franchise operation in less than three decades. Their success isn't a big surprise - the greasy spoon experience they offer is a cut above the rest in terms of atmosphere and quality.
Five Guys never freezes its beef, and the patties are hand formed, not from a factory. Red and white "minimalist diner" interior design, an order queue marked out by piled potato sacks, and open boxes of free peanuts in the shell (not a place for the allergic, they also use peanut oil for their fries), might be considered gimmicks or personality, depending on your perspective. The most memorable piece of non-burger personality is the complete and utter meaninglessness of their fries sizes. Whether you order the regular or large, they pour several scoopfuls into your bag.
If you're looking for greasy over gourmet, you won't do much better than Five Guys.