I enjoyed the first film, but felt like you could almost feel the edges of the film that couldn't be explored as it was written and designed with a certain budget in mind. Multi-million dollar movie, sure... but of an unknown, untested character with some pretty terrific weirdness behind it all.
But I really liked the three main protagonists, with Abe Sapien, Liz Sherman and Hellboy. The villains were bizarre and cool, and the threat appropriately apocalyptic for our hero to challenge.

Also, I believe Selma Blair to be sort of a fox.
Mostly, though, I think Ron Perlman is super great as Hellboy. I love the direct, uncomplicated guy who happens to be able to take on world-threatening baddies. All without a Will Smith "Ah, hell naw!" In a lot of ways, Hellboy is sort of a great stand-in for how I think many guys see themselves. Unpleasant, uncouth, and hoping their capable enough working with what they know to get the job done. But a totally different guy when it comes to dealing with their significant other.
The plot has an odd ring of familiarity as so many superhero films have been hitting the screen. A villain with a plan for ending the world, some personal problems, and a nick of time ending. In some ways, the plot of Hellboy II feels, in some ways, a little too much like the plot for Hellboy I, only streamlined. Instead, director Del Toro focuses on the dreamlike imagery you might remember from Pan's Labyrinth, presented on a grander scale.

This looks like the group shots of my prom pictures
And, really, no matter what else you might be skeptical about, Hellboy II is visually stunning. The dialog can be a bit clunky, and the action sequences a bit disorienting, but the creature scenes here are the best mass creature scenes since Luke Skywalker walked into a cantina.
I'm not guaranteeing its the best movie you're going to see, but its a good summer popcorn flick with surprisingly developed characters for a movie starring a red guy with an arm that came from Steelcase.
Del Toro might always have scripts that feel like they could be a bit more developed, but you have to salute him as a visionary. He's able to bring not just cool visuals (which movies like "Chronicles of Riddick do, and yet fail), but also a solid action film with a good deal of heart.