Hellboy: Blood and Iron is about vampires coming back after many, many years in wait, and also about ghosts and memory and all those things left behind. If it were about these things more-so in-depth (or rather the kind of attention that Guillermo del-Toro would pay to the subject matter if he directed), it would be really great material. Trouble is, the Hellboy animated movies, with this the second installment, are limited by means of budget, time, and even to an extent the scripting. There's a lack of the dry, sly and just outright clever humor from the Hellboy live-action movies, with only one or two quips from ol' Red (Ron Perelman, always good even in dull one-liners), and some characterizations and dialog that are as routine as whatever one might find in a straight-to-video release.
These flaws being noted, Blood and Iron is extremely enjoyable for what it can afford in its 75 minute running time, which is giving some lifeblood to a comic-book that needs it desperately. The plot works mostly upon the strengths of the animators, and luckily they are many. What might seem ordinary and traditional- even a little lacking in fluidity (again, budget)- gives way to extraordinary moments going past the expected for "kids" stuff. There's some very dark material particularly in this installment, as we see an iron goddess, a vampire curse, a couple of blasted witches, snakes, and those creepy ghosts (which, thanks to some del-Toro presence, reminds one of the Gothic folklore of Mexico). It's all very impressive when it works best, and there's even some interesting designs for these villains and creatures of the night.
There might not be much depth (the climax is just a bunch of "we are not like *them*" semantics from the iron woman to Hellboy as they punch each other senseless), but for a short while it's some good fun and some brilliant animation, for what it's worth. Less than great, and at the same time far better than it should have any right to be. A-