Excellent customer service.
I recently went to the Scottsdale Fashion Square location and ordered a small Cajun fry with my burger. I received a regular fry instead. Not really a big deal. I almost didn't say anything, but the Cajun fries are one of the reasons I go to 5 Guys, so I did.
The girl filling orders immediately apologized and said she would get my Cajun fries for me. I was satisfied with that. When I was called back up, she not only had my order corrected, but handed me a cash refund and an EXTRA bag of Cajun fries for my friend I was sitting with. I was shocked. You don't often see this kind of above-and-beyond service.
Five Guys is a no-nonsense restaurant. They do only a few things, and they do them well. I'm happy to include good customer service in the things they do well.