It certainly isn't literature but it is good occult/heroic/sucks-to-be-a-monster/adventure reading.
The movie maybe tried to be too grand and epic and really was at its best when it explored relationships. The many bit of humor, Hellboy eating cookies on a rooftop, THAT was classic Hellboy.
And really, as CAhobbit has said elsewhere, you NEED to go rent "The Devil's Backbone." It is smart and scary and leaves behind some indelible images. Keyholes have never been the same for me.