Still really like this, I get that it's divergent from the Hellblazer comic books but I think the tone and style of the film are great. In fact not having the film fawning over the comics continuity allows it to harvest the best ideas of the comic without being beholden to it, the result is a fun, and genuinely creepy, supernatural action film. Reeves isn't always the best of actors, but he always gives things 100%. He gives Constantine a great agitated energy and plays the character as just generally fatigued by the world he finds himself in. He's got a lot of presence in the film and he's helped by a supporting cast who are fantastic.
Gavin Rossdale and Tilda Swinton in particular are great as a snidey demon and conflict arch-angel. I kind of love Swinton in the role, because she's probably the closest you'll ever get to a live action anime character. Her entire attitude and nature are wonderfully conflicted, her desire to see humanity be better than itself combined with a brutal knowledge of what needs to be done. She's antagonistic and nurturing at the same time, genuinely pleased for Constantine when he becomes a better man even though he's just foiled they're plan.
Peter Stormare almost steals the show with his brief screentime. His variant on the devil is probably in my top three satanic performances (up there with Viggo Mortenesen and Peter Cook) and he gives the character a fantastic energy. It's one of those movies where I would have loved to have seen the series continue, just because the world created was so fascinating and Francis Lawrence demonstrated a fantastic cinematic eye.