This is a bit of a cheat since they have filmed Swamp Thing twice and had his own TV series. I will, however, say that none of these adaption came close to sheer invention under Alan Moore's writting. The original Swamp Thing was like a Soggy Wolfman. Forever the lonely monster longing for his humanity back. Alan broke that plot thread in the first issue he took over the strip with. In his version the Swamp Thing was not a man turned into a monster by chemicals and fire. Instead, there never was a man there at all. All of his memories were taken from the dead man but the Swamp Thing was always a botanical beast. This news first drove the Swamp Thing mad since he had for years hoped to become a human again. Moore's story follows how the creature picks up the pieces and forges an new identity for itself. An identity that would eventually bring the Swamp Thing close to godhood.
It's this heady mixture of high ideas and great characters that needs to see the screen. Audiences today are not the same audiences who in the seventies and eighties thought of comics only in the 4 color funny book way. We've seen some very mature works turned to film like "V For Vendetta" or "Road To Perdition." Audiences today would welcome our favorite veggie man with open arms I believe.