I just sent a review of the anthology The Sandman Papers to Strange Horizons. The review was a real struggle for me. Part of the problem was probably that I've never reviewed a work of criticism before. I had a little trouble writing about it and keeping it interesting. But it's primarily because something about the book kept nagging at me. Overall the book is pretty solid, and examines Gaiman's work on The Sandman in a variety of fun and interesting ways. But I kept thinking something was missing. It kept nagging at me and nagging at me, and I didn't figure out what it was until late last night.
Aside from two essays, the book barely addresses the visual side of comics at all. What a lot of people don't know is that a skilled comics writers, Gaiman in particular, does more than just write the narrative. They often give specific instructions to the artist, the colorist, the letterer, the panel designer to control the overall feel and look of the book. This puts Gaiman in a role similar to that of a film director, working with a variety of artisans with specialized skills but giving them guidance on how to use their talents. Not talking about the artwork in comics is like not talking about the acting in a film review.
It's a shame, really. Because the various critics do a really nice job discussing the narrative elements. I suppose it's because most of them, being english professors and librarians, are more familiar writing about narrative. Writing on the visual side probably just didn't occur to them, and the majority of exceptions to this rely quite heavily on Scott McLoud's book Understanding Comics. Nothing against McLoud, he's a great critic, but his book should just be a starting point for getting your head around the art of comics. Unfortunately, not writing about the visual side is an omission I see a lot in reviews for comics.
One critic I really think does it well, even in small review form, is Douglas Wolk. Aside from his own book Reading Comics he's done reviews for the Washington Post's Bookworld that are really quite thorough and well thought out. Here's a sample from his review Joann Sfar's Vampire Loves (taken from May 28 issue of Book World, page 9):
Sfar's got a charmingly distracted, scribbly visual style-even his panel borders seem perpetually on the verge of wriggling away-and his stories have a habit of meandering off on one tangent or another....The funniest sequences here, though, follow the strangely familiar social entanglements and petty frustrations of the undead; girls always go for the obnoxious werewolves, it seems.
In two short lines Wolk's given the reader a very good sense of not just the style of the story, but also the artwork and how the story flows. He's an excellent critic--far better than I am--but it's a level that anyone writing on comics should aspire to.
As to The Sandman Papers? I still recommend it if you enjoy criticism. Just be aware of the book's limitations.