I really really enjoyed this movie, despite all its flaws... and there were quite a few of them.
I liked how the film really expanded the universe, moving from the abandoned sewers and subways and into more lavish set pieces like the Elvish Underground, and Ireland. I liked how they made the BPRD feel like a real motley collection of freaks, a sort of ragtag band of people who do good because no one else can or will.
But sometimes, it felt like the film was at odds with itself in terms of tone. Everything involving the BPRD was laugh a minute humor --- Kraus beating the crap out of Red, Red & Blue singing Barry Manilow, Red being a big old adolescent jerk --- but every scene featuring the bad guys was just so serious and ominous that it felt like I was watching two movies at once.
Johann Kraus was probably my favorite character of the BPRD, but I didn't like the complete turnaround in character he made. Suddenly he just comes up to Liz, hints at his backstory, and he's with them in breaking protocol. There was also no real explanation as to why Abe would REALLY REALLY risk the End of Man by giving the crownpiece to the Prince.
Another plot hole was how the Prince didn't spirit his sister away when he had the chance after he unleashed a forest elemental, yet he did it after he speared Hellboy. In effect, it felt like the characters were bending themselves too much in the service of the plot, which itself is an excuse to move from one lavish set design to another and show lots of awesome creatures (and make no mistake, the design is wonderful).
But all those flaws aside, I still enjoyed it a lot. My girlfriend got into the Dark Horse comic because of the first movie, but I think we both like the movies more. They're just so much darn fun in terms of personality and character that its difficult to let their weaknesses overwhelm them.