This painting by Leonardo is definitely one mass produced and recognizable piece of art, I agree that is probably one of the most familiar Christian images today. one of my earliest memories is of my great-grand father and I, actually assembling  a pretty large jigsaw puzzle of "The Last Supper" that we glued together and now is framed and hung in my parents house. One reason why I like this piece so much is because it does show so much emotion is each of the apostle's faces when Jesus tells them that one will betray him. I agree that it is a good example of how High Renaissance artists progressed to humanistic and linear perspective qualities. I didn't realize he had decided to paint on dry plaster  instead of the usual tempera on wet plaster process and that is the reason it has gone through many restorations. Its kinda of sad that such a significant piece of art has deteriorated. Do you know how many times over the centuries it has been restored and if they are planning on anymore?