The movie starts off far more funny than the first Hellboy. This is very much in keeping with the quirky ad campaign that has been promoting the film (the inside the actor's studio commercial for example is quite funny). Hellboy is once again Ron Pearlman- the genius bit of casting that made the first movie so great is a huge win for any sequel. He's tired of working for the BPRD in secret and is going out of his way to be spotted by the real world. But a mythos of ancient elves is working to retrieve and unify some widgets to awaken a golden army of indestructible robots, and it's up to our heroes to stop it from happening.
The elven world is very much Del Toro's designs. Likewise, an extended sequence through a secret troll market hidden under the brooklyn bridge gives him a great canvas to paint his stylistic genius. And seeing the big and clumsy Hellboy smash through it is incredibly satisfying. The action sequences are all excellent, and the final robot battle is very fun and well done.
All the while this is done with some nice plot twists for the major characters. A love interest for Abe comes along. A new good guy is sent in from the BPRD to reign in our uncontrollable hero: Krauss is voiced by Seth Macfarlane basically doing his fish char from American Dad, but inside a wacky suit controlled by ectoplasm vapors. Selma Blair is back as Liz: they give her some good lines and a few good sequences, but she's mainly a support role.
So Guillermo Del Toro was able to work within Mike Mignola's world. He put his own thumbprints all over the work, and the whole comes out better than the sum of the parts. And this makes me all the more excited for the Hobbit, where I have all the same concerns: Tolkein and Jackson will give him even bigger shoes to fill, and now I think he can do it.