Guillermo Del Toro, the director, seems to have worked on the character giving it all the characteristics of and average girl stalking, jealous guy, however with a very high dose of attitude.
The make up consultant for Hellboy (Ron Perlman) ought to take away a lot of credit, though Ron Perlman seems to have done a good job on his part..Selma Blair has a pretty medium role with less lines and more special effects. John Mayers (Rupert Evans) has pretty much tried his best and played his innocent boy scout image to the character. However even though the performances are watch able, the story seems to hang around the horizon of unbelievable.
So if you really can take a good dose of fiction, the movie is worth a watch. Otherwise I would tell you to stick to some ground realities and choose something else to watch..