The preview focuses on a clash between good and bad, but it's totally not what you'd expect. It's more like a monster hiding just beneath the surface, using stuff like tech and social media to get even stronger. Instead of a regular war, the main problem is like a big "cleanse."
Even though he's pretty cynical and has gotten his hands dirty with the devil before, John Constantine is now the last guy standing against this mess. Looks like even the angels have thrown in the towel, so he's all by himself against this creeping darkness.
It also shows a different kind of bad guy using social media and the crave for eternal life – like a modern take on making deals with demons. People are basically selling their souls for online fame and the dream of immortality.