I think it is very hard to judge on the basis of photographs and portraits, as they can be very misleading. Having said that, I do agree that in some of the photographs the Empress does not look beautiful. However, there seems to have been general consensus among her contemporaries that as a young woman she was very beautiful indeed. Nevertheless, when her assassin was describing how he murdered her he commented that she was extremely ugly, so obviously her looks faded with increasing age.
I find Gisela attractive, I like her expression/eyes, so I suppose that beauty really is in the eye of the beholder.