One thing though.... how important do you suppose it would be to have seen the original "Hellboy" ?
Not very important at all.
They give a brief 2 minute recap of how Hellboy came to be here, on Earth and then jump to scene with him as boy and the movie rolls on from there. There is one brief mention of 1 character from the first movie for about 10 seconds but really seeing HB:1 is not a prerequisite at all.
Del Torro has not laid this out like Nolan has with Batman so your good to go and not worry about feeling lost.