There is a pretty comprehensive review at Yahoo! which is worth checking out. I found this information far more useful than the two reviews which I quoted below. If you don’t know what the movie is about, the synopsis on the Yahoo! site fills you in:
John Constantine (Reeves) is a world-travelling, mage-like misfit who investigates supernatural mysteries and the like, walking a thin line between evil and good. Constantine teams up with a female police detective, Angela (Weisz), who seeks Constantine’s help while investigating the suicide-like death of her twin sister. Does it have something to do with a mysterious group called "The First of the Fallen"? And what is it about Constantine that puts him in a position where he is making deals with representatives from both Heaven and Hell?
On the whole the effects were highly rated but Reeves’ acting left a little to be desired. The common complaint is that this movie lacks ‘heart’.
The Edmonton Sun had the following to say:
Constantine is a visually awesome but sadly empty spectacle. Once
again, a graphic novel/comic book has been transformed into a
special-effects-driven, live-action movie without heart and without a
clear narrative purpose.
For those of us who have never read Hellblazer, Constantine,
opening locally today, is a howling devil-dog of a movie all on its
own. That is because the story is garbled, the distorted religious
concepts in play are hokum and the pseudo-intellectual riptide could
drown you in drivel.
Worse yet, Keanu Reeves is awful.
Despite scoring 6.6 out of 10 on IMDB, the movie wasn’t too well received there either. One of the comments is particularly harsh:
Lousy and disrespectful adaptation of the Comic Book Hellblazer is a
travesty of a high order. Who ever thought that Keanu Reeve would have
been perfect as John Constantine should be fired for sheer in
competence. Keanu takes a great role and basically craps on it with his
lousy acting. Of all the actors involve, only Rachel Weisz and Peter
Stormare are able to transcend the horrible script, which manages to
contradict itself in the last forty-five minutes of the movie, and the
climax is a horrible joke in itself. The special effects were decent
but I have seen better on TV plus the plot is taken from an episode of
Buffy the Vampire slayer. They should have just called it Keanu The
vampire slayer instead, It would have made a better title.
I love these comic book adaptations so I am sure to see this one anyway, even though I expect to see Keanu Reeves playing Keanu Reeves, or at least a reprise of his role as Neo in The Matrix. Just a matter of what your expectations are, really.