Hmm...the film will be more campy than the comic, I imagine. One aspect of the comic's greatness is its ability to take many disparate elements (demons, paranormal bureau, Nazis, Lovecraftian creatures, gothic horror) and blend them into a seamless whole. A lot of that has to do with Mignola's artwork.
But the comic is campy too...Hellboy is always quick to point out when the depredations of a Kriegaffe (war-ape) are "total crap," and has a tendency to shout "BOOM!" when he hits something. There's no sound effect in the panel, just Hellboy yelling "BOOM!"
But really...the comic is greater than the sum of its parts. I wholly and completely recommend it.