What makes an interesting image?

What makes a interesting image? One you can go back to time and time again and not be bored with it? For me, some of the intriguing aspects of photography is discovering patterns you didn't know you were looking at with the naked eye. This image of the walls behind the Chase St. Warehouses is about rectangles and squares. Almost everything in this image is or is part of a rectangle or square. And when you boil those "chunks" down, what you really end up with is a whole picture of lines. Not necessarily a traditionally pretty picture, but an engaging one.