First things first. It’s been a few years since I’ve read any of the Hellblazer comics, and even then I only read the first couple of trades. I’m in no way an expert on the original material, so I can’t really speak to how true the show is to the source. What I can say is that it is far closer to the comics than the poorly executed Constantine movie. It is also very fun to watch.
For those of you unfamiliar with the story, John Constantine is an occultist who gets drawn into the war between Heaven and Hell. He uses his familiarity with the supernatural to (mostly) do good, as he struggles to make up for sins he’s committed in the past. He’s aided by Zed Martin (Angelica Celaya), an artist with certain psychic or prophetic abilities, and Chas Chandler (Charles Halford), who also has some strange supernatural characteristics…like being able to live through things that would kill a normal man.
Matt Ryan, a Welsh actor who has not had any major roles that I can find (and is also not to be confused with the quarterback of the Falcons), plays Constantine, and I think he does quite a good job with the role. He has the right kind of cynical, sarcastic, punk rock attitude that I associate with the character, and he certainly looks more the part than Keanu Reeves did.
In terms of tone I’d say the show is sort of a darker version of Sleepy Hollow, which derives a lot of humor from Crane’s being transplanted from the Revolutionary War into modern times. There is certainly humor in Constantine, much of it provided by our hero’s sardonic responses to basically every situation, but the deaths are more grisly (or graphic) and it seems that, at least so far, more bodies tend to drop during the course of case than happens in Sleep Hollow.
However, if you enjoy paranormal fantasy, especial of the demonic variety, then I definitely recommend checking this show out. The show is fun and the actors, especially Ryan and Celaya, deliver engaging performances. The last episode also saw the first appearance of Papa Midnite (Michael James Shaw), a voodoo priest who looks like he will have a recurring role as an antagonist, which will add a welcome dimension to the show and potentially add to its greater story arc so it can move somewhat away from being purely procedural.