A proper Constantine film wouldn't need that many such effect. Raising the tension, emphasizing the horror aspect, showing less, a slow build to the big climax, that's how to do a good Constantine movie, whilst allowing Reeves to do whatever he wants as the character---he's good enough to figure that out.
Honestly, the first film wasn't my cup of tea; but it wasn't bad as a movie, though of course not all that true to the comics.