NBC's Constantine was such a polarizing show, unable to grab ahold of any sort of footing on the network, the live action adaption of the Hellblazer comics was cancelled after only one season.
Though with some endings, some new beginnings can come with. Confirmed for Arrow season 4, Matt Ryan as John Constantine will be back as the Hellblazer himself, this time visiting Star(ling) City. Premiering in the 5th episode of the new season, the episode's title is "Haunted" and I can only guess what it will be about.
Here's hoping this can be a launching off point to save Constantine.