I have no familiarity whatsoever with the graphic novel upon which this film is based, so I can only address the film in and of itself. And I must say that I rather enjoyed it for the most part. Anything with angels and demons always interests me, and this film put a quirky spin on the agents of God and Lucifer. Since John Constantine seems to be a pretty tight-lipped fellow who doesn't reveal much of himself to anyone, Keanu Reeves seems like a pretty good pick to play the part - there's not too much acting required for this one.
So what's this all about? Well, John Constantine has this gift (or curse) to see and interact with creatures from both heaven and hell; he's already been to hell and back once - literally - and therein lies his biggest problem. Since he did commit suicide, he's not eligible for a ticket to heaven later on - and this second life he was given is hurtling toward an impending end thanks to all those cigarettes he's chain-smoked for years. He's content to go his own moping way, dealing with particularly difficult exorcisms when called upon and generally just bemoaning his awful fate. Then a female cop (Rachel Weisz) shows up asking for his help; her sister supposedly committed suicide, but she doesn't believe it. Both Rachel and her sister were pretty special, for they could also see the things Constantine sees (although it takes some rather intense training for Constantine to reawaken those abilities in his new, temporary partner). It soon seems obvious that something big is going down. More and more demons are trying to cross into our world, violating a big treaty between God and Lucifer (who would have thought that demons couldn't be trusted?), and that just doesn't bode well for anybody. Before you know it, special effects are coming at you left and right, and the birth of the Antichrist is almost at hand.
Now, you're probably thinking that old Mr. Pitchfork himself is behind the whole Antichrist thing - but that ain't necessarily so. The movie manages to throw in a couple of small surprises toward the end (although it certainly breaks no new ground in showing Lucifer as a really stupid being). I really hated the characterization of the angel Gabriel, though. First off, I just don't see Gabriel as a woman, but more importantly, this Gabriel comes across as a far from superior being. This isn't the first time we've seen a Gabriel who hated and conspired against humans (out of jealousy), but Constantine's Gabriel is a far cry from a similar archangel in, for example, The Prophecy.
The plot of this movie isn't all that bad, but it could have been told much more effectively. If you're not into this kind of weird subject matter, you may look upon the story as little more than an excuse to throw some impressive special effects together. I'm giving Constantine a somewhat tentative four stars, but I'm sure there are a good many people who won't enjoy the film very much at all.