Definitely love the skull with the empty eye-sockets. The skull is a powerful and evocative symbol, and features heavily in Giger's artwork.
But I think where it's really important is highlighted by that old quote from O'Bannon:
QuoteCobb's monsters all looked like they could come out of a zoo --- Giger's looked like something out of a bad dream.
It's the detail, sometimes barely visible, that hammers home the nightmarish quality of the design and appearance.
I don't mind them losing it for the other films -- because ALIEN was a nightmare and a horror film and it works so well for thematically -- and the other films treated it more like a dangerous, predatory animal and so it becomes an element that would actually be at odds.
I like the artwork above. Very scratchy, like Clive Barker's art.