John Constantine is one of if not the best fictional exorcist out there. And one of my favorite characters of all time. And this story arc showcases his persona perfectly.
Although it would be nice to have some context before reading it you still can manage without it and just googling the basic info on him.
The story starts off with John coughing up violently. Worried he checks himself into a hospital where he finds out that he is suffering from advanced terminal lung cancer. Which sadly is no surprise since he smokes dozens of cigars daily. This breaks him down because it is something that he can never fix. He is a cunning bastard who can get out of any trouble but yet all of his tricks and magic can not get him out of this.
He tries contacting old acquaintances, speaks with doctors and does whatever he can but at the end of the day nothing helps. And this takes a huge toll on him. It is only when he has an encounter with the devil (who has a personal grudge against him) while visiting his old friend he remembers that the only person he can rely on is himself. Thus he devises the riskiest plan ever in order to save himself.
Now, I usually don’t like spoiling things but even as I am writing this I am so tempted to explain what happens but at the end of the day it is better to find out for yourself rather than reading it from some place. It is absolutely insane. While the first part of the series shows him at his lowest, the ending shows him at his finest where he does one of the most impressive feats in comic book history (in my opinion of course). This balance is what makes him such an amazing character.
The art may not be the best, it is not the selling point of the comic but it is still decent enough to make you stick around, and in some cases actually help the story (if you read it you will know what I mean) but the writing is just insane. And of course it is amazing since it was written by Garth Ennis. It is definitely something that one should read even if you are not into Hellblazer.
The way in which the story is concieved that you can see the entirety of his persona in such a small package is amazing. It is no wonder that this is the most well known story of the series. It was even very loosely adapted in a movie but it did it no justice.