Back in the days when I read comics regularly, I was a big fan of the Alan Moore Swamp Things and it introduced the character of John Constantine. He then got his own comic, Hellblazer which I began to read at the start. On a primary level, Constantine is blond and British.
So when Keeanu Reeves pops up speaking a decidedly American accent and with his trademark dark hair, you know something’s amiss. In fact Constantine doesn’t deviate massively from the mood of the comics, but it does commit the cardinal sin of being dull.
I’d explain the plot, but it really isn’t worth bothering with. He hooks up with Rachel Weisz and lots of CGI effects ensue. To give it’s due, the effects are first rate, but overall it amounts to not very much. It’s just dull.