Watchmen and the Comics Medium
Many of the scenes in Watchmen are clearly cinematic (particularly the opening pages), and comics defenders have traditionally invoked the cinema as a model for an audiovisual art form that is taken seriously, even as comics scholars have more recently explored the limitations of the model.  But Moore has stated repeatedly that his primary interest in comics creation is do something that cannot be done in any other medium. In this light, Watchmen serves as Moore's manifesto.
Two elements of Watchmen defy a facile comparison of comics and film. The first is the narration itself. The book has multiple narrators, each of whom take a turn providing the rough equivalent of a voiceover in captions at the top of the panels. Rather than comment explicitly on the action, these narrative streams more often run parallel to it, creating an aesthetic effect based precisely not the juxtaposition or counterpoint between the captions and the pictures. The sheer density of information would overwhelm film, but is manageable in comics, where the reader controls the passage of time.
Nowhere is this more jarring than in the Tales of the Black Freighter, the pirate comic whose narration has no direct connection to the overall plot, serving instead as a thematic or allegorical double to the outer story. By the end of Black Freighter, the careful reader will have seen that the story could be a critical commentary on Adrian's actions, and on the very idea of intervention and heroic rescue.
More spectacular are the chapters that feature the second element that defies the power of cinema: Jon's fourth-dimensional perspective on reality. Chapter IV is devoted entirely to the life and times of Jon Osterman, but the times are far more intriguing than the life. A physicist accidentally transformed into a god-like superbeing, Jon experiences life roughly the same way as the hero of Kurt Vonnegut's Slaughterhouse-Five. But where Billy Pilgrim is "unstuck in time," bouncing back and forth through his life seemingly at random, Dr. Manhattan is perfectly at ease with his fourth-dimensional perspective.
To Jon, time is not linear or sequential, but (in echoes of the physics problem at stake in Ursula K. Le Guin's The Dispossessed) simultaneous. All moments happen at the same time, and can be viewed or experienced in any order. Certainly, the comics page, with its sequences of juxtaposed panels organized on a plane, serves as the perfect vehicle for conveying Jon's experience of time; while it is possible to skip back and forth among the pages of a prose novel, it is far more disorienting. But far more intriguing is the possibility that Jon essentially views all time as does a reader reading a comic book. Jon's defining superpower turns out to be "comic book vision.”
Watchmen and the Superhero Genre
Moore and Gibbons do not content themselves to creating a metafictional exploration of their chosen medium--they insist on doing so within the confines of a genre that is easily dismissed as adolescent fantasy. In particular, Watchmen subtly plays with the notion that both superhero stories and comics are dangerous to their consumers.
One of the many threads running through Watchmen is the disappearance of cultural figures from a wide range of fields, all of whom are kept on a secret island by Adrian Veidt. Not long before the "invasion" of New York, we see that the writer of Tales of the Black Freighter has been on the island, having an affair with a painter. It is the combination of his horrifying words and her disturbing images that forms the content of Veidt's psychic attack on New York. Those not immediately killed by Veidt's action are driven insane when confronted with horrific words and pictures. Ironically, Frederic Wertham, the 1950s psychologist who helped convince congress that comics were corrupting the nation's youth, turns out to be correct: by the end of Watchmen, comics have led to madness.
In Watchmen, it is superheroes who are directly responsible for both hastening and forestalling the apocalypse. Moore and Gibbons locate the origin of the modern superhero in the destruction of Hiroshima by an atomic bomb; this is the event that causes Jon Osterman's father to insist he study physics. The atomic age is obliquely what brings together both the perfect, Apollonian body of Dr. Manhattan and the paunchy frame of Daniel Dreiberg. It is telling that a book featuring so many near-perfect bodies keeps returning to the figure of the fat man. It is a fat man who steps on Janie Slater's watch, inadvertently starting the chain of events that leads to Jon Osterman's disintegration and reincarnation as Dr. Manhattan. It is a fat man whose body must be mutilated in order to unlock the door of Rorschach's prison cell. And who can forget the perversely light-hearted code names given to the atomic bombs the United States dropped on Japan: Fat Man and Little Boy. The archetypal weapons of mass destruction sound like a bad parody of DC’s dynamic duo.
Finally, it is a particularly abject fat man, Seymour, who, thanks to his job as an editorial assistant at Rorschach's favorite right-wing rag, ends up in the position of ultimate arbiter of the novel's fate. The red-headed, freckled Seymour, who looks like an overweight, funhouse mirror version of “Superman’s Pal, Jimmy Olsen,” wears the Watchmen smiley face on his shirt. And why wouldn’t he? A mentally limited, grotesque analog of a classic comicbook reader identification figure, Seymour is the stereotypical fat fanboy imagined by the medium’s detractors as the average consumer of superhero entertainment. The second to last frame of the book shows Seymour's hand hovering over the slush pile that contains Rorschach's diary (and the secrets of Adrian Veidt), accompanied by the editor's words "I leave it entirely in your hands.”