The first thing I think of when I remember our trip to Five Guys is "loud". It's not really the music or the customers either, it's the employees working in the kitchen hollering back and forth.
Getting to the food... it's good, not out of this world. I'd rather make a burger on the grill at home. Their fries are the real selling point for me, very tasty!
Oh and I love those pop machines, very fun...just don't get stuck behind a group of people who have never seen one before...you'll be waiting forever.