I wouldn't say Kevin Nowlan is producing bad art now, however the cover is less than steller (imo) and that does happen, they all can't be great. However, I do blame the editors today since they are the ones who approve which cover is to be used. An artist will sketch out a few different covers and the editor will pick the one he feels best suits the story inside, and most editors pick the wrong one. Just cause the artist doesn't "draw pretty" doesn't mean they are bad comic book artist, the main objective of a comic book artist is to tell a story through pictures in a sequence so the story will move. That's what makes Frank Miller so good. Do you really think the art in The Dark Knight Returns looked good? Not really, but everything else was awesome.