Past attempts to adapt Swamp Thing haven't come close to the epic scale and smart storytelling of Moore's run on the comic. In order to capture some of that intelligence, I think this adaptation needs to be a high-budget prestige television drama. I think it would be a great fit for HBO in the eventual post-Game of Thrones era.
We can do a flashback to Swamp Thing's origin, but the show should begin its adaptation with Saga of the Swamp Thing #25, in which Swamp Thing has accepted that he's not Alec Holland and that's okay, Abby has just gotten a job working with troubled children, Matt Cable is in a very bad place, and Jason Blood wanders into town to stir up trouble.
Season One will cover the Monkey King story, the return of Anton Arcane in Matt's body, and Swamp Thing's first journey into the afterlife. Along the way, other characters from the spooky side of DC Comics will appear. If there's a Season Two, John Constantine can show up and lead into the American Gothic storyline.
Alexander Skarsgård as Swamp Thing/Alec Holland
My original plan was to cast different actors as Swamp Thing and Alec Holland. They're not the same person, after all. But then I realized that Skarsgård is tall enough to play Swamp Thing, looks like Alec Holland, and is talented enough to do both.
Tatiana Maslany as Abigail Arcane Cable
Orphan Black has taught us that Maslany can do basically anything, and with any color hair. She can definitely pull off the weird energy and weird hair of Abby.
Joseph Gordon-Levitt as Matthew Cable
Matthew spends most of this season possessed by the evil spirit of Anton Arcane. An actor's actor, Gordon-Levitt will be great at letting those little hints of evil spill out before he goes full-on demonic for the climax.
Rutger Hauer as Anton Arcane
Joseph Gordon-Levitt will carry most of the weird of the Arcane performance, but for flashbacks and ghostly visions, who better to embody Anton's original self than a legend of genre film creepiness?
Mads Mikkelson as Jason Blood/Etrigan the Demon
When he appears in Swamp Thing, Jason Blood's demonic alter ego has blended into his personality so deeply that he's just as demonic in his human form. That's exactly Mikkelson's wheelhouse.
Taye Diggs as Deadman
The way Deadman is always drawn moving while he floats in midair says to me that whoever plays him should be trained in dance. Taye Diggs has that, and he comes with a memorable face and a bald head!
John Hawkes as the Phantom Stranger
The first word that comes to mind whenever I see Hawkes' face is "weary," and that's totally the Phantom Stranger's brand.
Dwayne Johnson as the Spectre
The first time the Spectre appears in Swamp Thing, he's a huge intimidating figure who erupts startlingly into genuine laughter. Rereading that moment, I knew he had to be the Rock.