Ron Perlman is great as Hellboy. I never saw the Mike Mignola comic books on which this movie was based, but that didn't seem to matter. It was a cool monster movie, action movie, and Good vs. Evil move. Cool special effects.
The Abe Sapien (fish guy) character has the unmistakable, but uncredited, voice of David Hyde Pierce (Niles Crane, on the TV show Frasier).
Lots of elements here borrowed from other films, notably Kroenen, the Nazi assassin with the mask and the breathing, reminded me of a svelt, capeless Darth Vader. The scene with the wounded Abe Sapiens floating in the tank with tubes attached was right out of The Empire Strikes Back, in the part where Luke is recovering from the abominable snowman attack. The cool, lion-like, tentacled monsters (Sammael) reminded me of that forgettable, but entertaining monster movie, The Relic.
Incidentally, I, Robot preview with Will Smith looked really cool. That might be an interesting book to read. Sophisticated, mainstream robots are definitely in our near future if technology continues at its present pace.