I didn't enjoy this sequel as well as I did Hellboy (though I have to admit that I watched it at 1am, and that could have contributed to my disappointment). The first film had a much deeper message and really got me excited to see this one. Though somewhat disappointing because of the story's lack of depth, I was thoroughly entertained and particularly liked the more martial arts type of fighting in the Golden Army.
You have your classic struggle between good and evil, and good ends up winning (of course at the very last moment). Prince Nuada's plan to destroy the humans and perpetuate the race of magical creatures (particularly his, that of Elf) which seems to be the plot of a lot of sci-fi movies, was not terribly original. For some reason, genocide is honorable in the eyes of a being who believes himself to be more elite and deserving of life on this planet than the weak and greedy humans (one movie that comes to mind is Sky Captain and the World of Tomorrow).
I thought the dry humor was great in the first one, but was over done and almost stupid at times in this one. I had to roll my eyes when Hellboy and Abe got drunk and started singing love songs. For some reason the critics loved it. If you're looking for a fun, action packed, sci-fi movie, this could be it, just don't expect to be enlightened.