In-N-Out is a cool place, and I love that you can see the potatoes being peeled, and I also love their miniscule menu.
Part of its attraction is that you can only get it in certain parts of the country. It's the same pull that Juengling beer has (it's tasty, but its limited geographic availability is part of its draw. Coors used to have this advantage as well, but no longer obviously).
I'm a vegetarian so I cannot comment on the quality of the burgers. I do like In-N-Out's milkshakes.