Now that the official trailer is out (see above) I'm full of cautious hope about the quality of Zach Snyder's adaptation of Alan Moore and Dave Gibbons' graphic novel Watchmen. As 'Watchmen' Trailer to Comic Comparison at Ropeofsilicon.com shows, the colouring has a darker, metallic, Gotham City flavour compared to the book, but many of the scenes in the trailer have been storyboarded closely on the original, and it looks overall highly atmospheric. (The trailer leads with the nuclear accident that changes Jonathan Osterman into Doc Manhattan, the blue CGI character shown later).
The Hugo-winning Watchmen is, deservedly, a classic of graphic novels, that both celebrates and subverts the superhero genre. At one level, it's a whodunnit: a government operative is murdered by defenestration, and suspicion falls on his past associates, a disbanded alliance of generally dysfunctional costumed crimefighters. The scenario, however, is complex; it's set in an alternate 1985, in a world whose 1950s saw the beginning of two generations of costumed crimefighters using the usual mix of athleticism, martial arts and technology. This status quo has been shaken up by the 1960s creation of a genuinely superhuman hero, Doc Manhattan, whose godlike powers over matter and energy have enabled Nixon to win the Vietnam War and caused many subtle differences from our world such as a decline of petroleum economy (as he can synthesise unlimited lithium for batteries).
The storytelling is also complex. The main narrative is intercut in some places with that of a pirate comicbook, a form that dominates in this alternate world. It's interspersed with pastiche memoirs, case notes, monographs and features (for instance, on Max Shea, a leading comicbook artist who has gone missing). And in part it's told in a non-sequential stream-of-consciousness form from the viewpoint of Doc Manhattan, who sees all time segments simultaneously and whose increasing psychological estrangement from humanity becomes a major factor in the story. Furthermore, Watchmen is rich in verbal and visual cultural allusions (right from its titular reference to Juvenal's Sed quis custodiet ipsos custodes) and is an extended exploration of the conflict between characters who apply radically different moral stances - such as uncompromising Biblical-style retribution, utilitarianism, and cynical nihilism - to the same aim of "doing good". Many of the characters are thinly-disguised heroes from Charlton Comics (a low-budget publisher that folded in 1986 after selling its characters to DC), and Watchmen can be read as an allegory of how superhero comics reflect the era of their creation, from naive two-fisted Golden Age heroes through more complex and flawed Silver Age reimaginings to postmodern angst.
All in all, it's a tour de force of the comicbook form that lives up to Alan Moore's intention to create "a superhero Moby Dick; something that had that sort of weight, that sort of density". I'm certain that some of this complexity will necessarily be removed from the film. Nevertheless, the basic storyline appears to be faithfully followed. There's more on the whole movie project at Watchmencomicmovie.com, which has further photos. If you've read Watchmen, or don't mind spoilers, The Annotated Watchmen provides a concordance to its many allusions.