Zack Snyder, director of 300 and Man of Steel, also helmed the film adaptation of Alan Moore's Watchmen. What's "important" for purposes of this little spiel is Terry Gilliam (Brazil, Fear and Loathing in Las Vegas) also attempted to make Watchmen, twice, but eventually gave up, deeming the comic "unfilmable."
Well, not *this* necessarily.
Here's what you need to know about Watchmen: it takes place in an alternate reality where we won Vietnam -- thanks to the godlike Dr. Manhattan -- and Nixon is still President (in the 1980s), yet tensions between the U.S. and Soviet Union have brought the world to the brink of nuclear war. Until, that is, the brilliant Ozymandias devises a diabolical hoax to convince the superpowers to work together for peace. The ending of Moore's story finds the heroes (well, most of them) agreeing to further the deception for the better of mankind.
Enter producer Joel Silver, who gave an interview to ComingSoon.net in which he describes what might have been, had Gilliam gotten the green light (hint: this is what Snyder takes issue with).