Now, unlike the Marvel movies, I was unfamiliar with the comic book antecedents of the Hellboy films, and have not seen the first one all the way through (I've seen bits and pieces when it's been on TV). So, I was in a position of really wanting more "backstory" here. I recalled the basic story of the main character, but a lot of the others were a bit of a mystery to me.
The mythic elements of the plot here, however, were fascinating ... going back to a time when Humanity battled against the Elves, Trolls, etc., and ended up with a truce, but only after the Elves/Trolls had developed an indestructible mechanical army (4,900 of 'em) made out of gold. The prince of the Elves was not happy with the truce, and has been off sulking over it (while practicing his martial arts skills) for millennial. Deciding (for no discernable reason) the time is right to kick humanity's ass, he sets out to re-assemble the 3-part crown that controls the army which is in hibernation somewhere (if the Elves are still around from back then, why don't they know where the location is?)..
Of course, most of this (except the hidden army, of course) is happening right under Manhattan.
As a long-time student of archaeology, etc., there were some enticing concepts involved, but some whoppers as well (in the early auction scenes, a huge statue was a copy of 4.5"-high "Venus of Willendorf" figurine ... I mean, if you're going to use something so recognizable, why go completely out of scale with it?). The best parts of the movie had a "Men In Black" feel to them, of this whole world existing beneath New York that nobody knew about (or, in this case, could see without special arcane headgear).
Of course, the occultist in me would LOVE to get into the library at the center where Hellboy and friends are based (the "Bureau for Paranormal Research and Defense") ... and was rather distraught to see the field box of Hellboy's "father", Professor Bruttenholm, dragged into the site of the early carnage and neither protected not obviously retrieved when things got ugly.
There was a lot of romance going on too, but I thought it was handled far better than in, say, the Spider Man or Hulk movies ... probably because the "love interests" were kick-ass mutants and/or non-humans.
Despite my constantly wondering what exactly was going on, I really enjoyed the movie, which was rich with both constant action, humor, visual depth, and "moral themes" (which hearkened back in places to Roy Batty's exchanges with Deckard in Blade Runner). I sure liked it better than that WALL-E turkey we saw a couple of weekends back (I've also recently seen, but not reviewed Kung-Fu Panda, Get Smart, Iron Man, and The Forbidden Kingdom, all of which were pretty good)!