Any form of restoration is impossible without criticism. The cleaning of the Sistine led to outrage by several art historians who like many others had grown accustomed to the dark, somber frescos. When the brilliant colors of the paintings were revealed they twisted themselves into knots attempting to offer arguments as to how the darkness was not due solely to centuries of soot and candle smoke, but that Michelangelo must have glazed over the completed frescos with oils and varnish. And these were art historians who should have known better... who argued that Michelangelo would never have used such brilliant, saturated colors... in spite of this painting...
... and in spite of the brilliant, saturated colors employed by the Mannerist followers of Michelangelo.
So now they are moaning that the Van Eyck lamb doesn't look like it long did... over-painted by earlier "restoration" attempts?
Even in this small, low-resolution reproduction, you can see that the ears were originally quite a bit lower and the eyes moved. The more human-like face would be quite common in images of animals from the late Gothic/early Renaissance. The human aspect of the face would also make sense considering the symbolism of the Lamb as Christ. The more natural lamb may be more immediately pleasing to our eyes, but that is in no way a measure of whether it was more accurate to the intentions of the painter.
Over the Christmas holiday, I visited the Cleveland Museum of Art where I was particularly taken by the jewel-like paint-handling of this painting by the contemporary/follower of Van Eyck, Petrus Christus...
You almost needed a magnifying glass to see all the details... let alone to have painted it. I would certainly love to see the Van Eyck altarpiece when the restoration is complete.
ps. After posting this I noticed that the lamb in Petrus Christus' painting exhibits similar frontal eyes to the restored Van Eyck.