In point of fact, the main narrative, involving the plan of the elf prince Nuada (Luke Goss) to take humanity down a peg or two by reactivating the army of juggernauts that imposed a truce on the humans in prehistory, is fairly linear. Where the movie gets complex is in the character interactions: Hellboy with/vs his floundering boss (Jeffrey Tambor), with Liz Sherman (Selma Blair), and the new team member, Johann Krauss (voice by Seth McFarlane). Then there are the relations between/among the other group members, and that of Abe Sapien (Doug Jones) with Princess Nuala (Anna Walton). These 'soap opera' elements are familiar to fans of the comic, where the profoundly disfunctional B.P.R.D. team are sometimes literally their own worst enemies. But hey, isn't one of the usual criticisms of comics-based stories that they lack character development? So, give the audience lots and you still get complaining--some people are never satisfied.
Part of the interest of the story is that technically, Prince Nuada has right on his side: the humans HAVE broken the treaty. He's just determined to be TOO ruthless about redressing the balance. Goss as Nuada is a formidable foe in himself. He has the strength, speed, and martial arts chops one might reasonably expect of a near-immortal elf lord, plus a nifty magic weapon. With his chalk white skin and fine scars, he is almost an "Elric"-like figure, or what you might get if Legolas became "The Crow." He is well supported by Walton as the tragic Nuala, who is mystically bound to her brother but does not share his zeal.
Ron Perlman recreates his role as Hellboy with with all the thickheaded gruffness one would want, plus a tender side we seldom get to see in the comic books. After all, Hellboy's main strength is, well, strength, and that he's so far proven well-nigh indestructible. "Blunt instrument" is a term that suits him well in a number of ways. Doug Jones, who plays a couple of other 'creature' roles as well as Abe Sapien makes the gill-man a sensitive character, struggling with unfamiliar feelings. Selma Blair is very good as the conflicted Liz Sherman as well.
The other real star is the design of the picture, heavily influenced by director/writer Guillermo Del Toro. Lead by the ectoplasmic man, Johann Krauss, in his diving/containment suit, the supporting cast includes a legion of trolls, fairies, gothic angels, and the golden golems of the Army of the title, all beautifully and grotesquely realized.
One minor quibble: when one knows as much about myth and legend as Hellboy creator and film co-writer Mike Mignola and Del Toro evidently do, why make changes that don't make either sense or difference to the plot? The name of Nuada and Nuala's father is given as Balor. Well, OK, in Celtic myth Balor was actually an enemy of Nuada and not his father, but the character needed a name, and perhaps we don't recall the truth, eh? Except that Balor is referred to in the beginning narrative as the "One-Armed." Eh? Balor is famous as the "one-EYED" in myth. It is Nuada who loses an arm and becomes known as the "silver hand" (Nuada Airgetlám) for the miraculous artificial arm he acquires. I can see for plot reasons why that wouldn't work in this story, but why transfer that attribute to Balor, especially when, any time we see Balor, he appears to have two arms and the story of the replacement doesn't come into the movie? But this is nitpicking.
Very good fun, and more enjoyable in a lot of ways than most comics-based movie fare. Recommended.