During Casey's run at Marvel Comics people started to recognize his talent as a writer, especially in regard to his work on the book Cable. He took the story in a different direction than had been previously established. Cable went from a multi-gun toting tough guy to a more spiritualized leader for the Askani.
Casey wrote many titles for Wildstorm comics, often to high critical acclaim, like the highly experimental Automatic Kafka with artist Ashley Wood. Casey took over Wildcats and gave the series new direction turning from standard superheroics to corporate espionage. His Mister Majestic series with artist Ed McGuiness impressed DC Comics enough to offer them a run on Adventures of Superman.
Casey wrote a limited series for Marvel Comics, a sequel to 2005's Avenger's: Earth's Mightiest Heroes. He also wrote the series G.I. Joe: America's Elite for Devil's Due Publishing and Gødland for Image Comics. He is also wrote a revamp of the original Youngblood miniseries by Rob Liefeld, called Maximum Youngblood. Recently, as well, as discussing the ending of Gødland and the new Charlatan Ball and Nixon's Pals, he mentioned that Codeflesh would be returning.
Currently, he, along with the rest of Man of Action, is one of the executive producers of the Ben 10 reboot.