She found it eerily creepy. I guess I have discounted it because I have in mind the medieval manuscript image. It actually looks better in the web version than on the book jacket -- it looks too fuzzy on the book.
Ironic, because the book is all about image: the vision of the Green Knight when he arrives amid the Yuletide revels; the image of perfection that Gawain's shield represents, a pentangle on one side and Mary on the other; the picture of the perfect chivalrous knight that Gawain finds burdensome when he's face to face with an avid reader of romances and doesn't feel up to the role; and the picture of heroism that Gawain measures himself against -- and finds he is lacking.
I usually can't be bothered with Arthuriana -- it's the one part of medieval literature I really can't abide (perhaps because it's so popular? after all, ask anyone what they know about the Middle Ages and they will quickly come to Arthur), but I really enjoy SGGK. Perhaps it's the deliberately archaic form the poet chooses -- he even alliterates in good old Anglo-Saxon style. Perhaps because it pokes holes in the absurd ideals of chivalry, ideas that probably never existed in reality at all. Perhaps it's because the characters seem aware of all those pressures and still make mistakes -- but the poet, rather than harshly judging them, treats their failures with compassion and good humor. It's an attitude some modern Christians could well imitate, in contrast to the public face of their religion at present, which is all about judgment and accusation.
All too often people look at the Middle Ages as "Dark Ages" of ignorance and superstition -- when all you have to do is read some of the texts to find a world much like our own.