I wouldn't say it's crap, they at least tried to get close to the source material. But it's too campy to be a proper adaptation (some of the stories that they adapted were much darker in Constantine. They were most likely toning it down for primetime TV.)
Also, they went overboard with the special effects but used cheap special effects that wouldn't look out of place in Buffy the Vampire Slayer. It's sad because the stories in Hellblazer could have benefited from less flashy special effects. They could have gone with atmospheric, like Oren Peli's the River.
They also saddled it with a poor timeslot and relatively weak marketing.
