Even if “Constantine” doesn’t last more than a couple of weeks on NBC, it’s still better than the 2005 feature film with Keanu Reeves also based on the Hellblazer comic books. There’s good stuff in the pilot — the special effects, for one — and not-so-good stuff, leaving the question up in the air about whether writers David Goyer and Daniel Cerone, who developed the series, can make the fixes necessary to do justice to Hellblazer. Constantine knows that Liv is being pursued by evil forces and makes it his job to both protect her and help her understand how to use the special gift she possesses of being able to see otherwise invisible demons all around us. Ryan certainly looks the part of a tortured “master of the dark arts,” but otherwise, there are sporadic credibility gaps in the pilot that need immediate attention.