Alan Moore warned that “Watchmen” was unfilmable. Zack Snyder (“300”) didn’t believe him.

He probably does now, having delivered such a lengthy, visually dynamic and convincing lesson on how not to adapt a graphic novel. Don’t worry, the basic steps are much easier to follow than the film. First, come up with a creative and memorable opening sequence, but then don’t bother maintaining a comparable quality for the next 160 minutes (momentum will naturally do it for you). Instead, imitate the original slavishly and obsessively, but change the ending for something far less effective and logical. It’s probably not that important anyway – Moore only spent twelve chapters driving at it. Art-direct the hell out of the movie because then it’ll automatically reflect the mood of its source. Choose miscellaneous overused tunes for the soundtrack, regardless of whether they actually fit the scene (does awkward, costumed sex deserve a “Hallelujah?”). Finally, by all means give the film that flashy, mind-numbing blockbuster feel, lest anyone be tempted to ponder too hard any social commentary it happens to contain.

The result should be about as dull and disappointing as “Watchmen.” Snyder’s creation drags on forever without giving its characters enough room for development. It ambitiously attempts to follow as many storylines as possible, but gets lost in its own narrative labyrinth. And the original’s rich political subtext? It’s in there somewhere, but the film, too busy drowning in the complexity of Moore’s dystopian universe, fails to keep a firm grip on it. Thus, “Watchmen” never goes beyond being a pale copy, albeit a faithful one – it paints the primary colors right, but botches the shading.

Not to say that its shortcomings will only affect those familiar with its source material. To the uninitiated, the movie comes across as even more convoluted, nonsensical and unremittingly tedious. It’s form over content, with a vengeance.

Too bad Zack Snyder couldn’t figure out that this isn’t Sparta anymore. Without the skill to back it up, directorial hubris is like the Doomsday Clock: it only foreshadows impending disaster.