I've seen Constantine three times and I enjoy it more each time I watch it! It is truly well-done and extremely entertaining, and I can guarantee that if you like horror, suspense and/or fantasy you will love this movie! Keanu Reeves plays a very cool Constantine, who is a modern-day exorcist but most certainly not to be confused with a priest, as he has his issues and a burden of sins from his past that he carries with him. Constantine is a very realistic and human hero who is devoid of superpowers but has all the cool gadgets and the kick-ass attitude needed to survive in a world slowly being invaded by demons and scheming angels. He meets Angela (Rachel Wiesz) after she loses her sister, Isabel to the forces of evil. She comes to Constantine in search of an answer on where Isabel has ended up following her apparent suicide. Constantine journeys to other realms/dimensions in an attempt to get those answers, even paying a couple of visits to hell. Needless to say, with such a plot the special effects, acting, sets, script and even wardrobe have to be carefully conceived and executed to make it believable, and they are... in spades.
Constantine achieves what all great movies always do: it takes you into another world that makes you forget everything about your own world the whole time you are watching it. And really, in the end, isn't that what great cinema is all about?