What a surprisingly striking cover. The lack of a background could have made it overly simple and dull looking--but instead, the all-black background makes Namor and Thing pop off the page, and I think heightens the tension (with some help from the dramatic blurb).
Buscema also does a gorgeous job with Namor's muscular bod here, and I think the colourist deserves a shout out too--the shading really enhances Buscema's great work here. Ben Grimm looks great too, but this is a particularly impressive image of Namor, imo.