Something about the recipe for the chicken patties being fried up really works well. McDonald's has tried to duplicate it with their "Southern style chicken sandwich" in some markets (which at least is a step up from the awful McChicken), but hasn't gotten the formula quite right. Would not be surprised if the proprietary part wasn't very bad for you.

Waffle fries also are semi-unique...others could try to duplicate, but it seems that if you make a splash initially with one type of fry you have to stay with it. So McDonald's is known for the straight and narrows, Arby's for the curly fries, and Chick Fil- for the waffle fries.

They had a good banana-pudding flavored shake about a year or so ago.

The notable thing about Chick Fil-As around here that never ceases to amaze me is how long the drive-thru lines will get, i.e. how long people are willing to wait (and use gas) in that line rather than get out of their cars, SUVs or whatever. Inevitably they will be behind someone with a large order or with something they don't have already prepared and get a delay, so from a time perspective the drive-thru is a terrible choice. Chick Fil-A isn't the only place I've seen people make horrible time trade-offs by being in the drive-thru, but I think it's the worst (i.e. longest lines of cars).