I think what makes five guys burgers so awesome is not the patty, but the melted cheese and the variety of toppings and sauces that are free of charge. I've always stuck with the little burgers cos that's more than enough for me (with all the toppings).
Must try the Cajun fries. What's best is they always top it off with an extra scoop of fries regardless of which size you order.
Seating is alright, it's a fast food restaurant after all. Drinks are refillable. They also provide unlimited peanuts while you wait for your food.