Early review from from a fanboy (NO SPOILERS)

Rating: 6/10 (10 June 2014)

I saw HTTYD 2 at the LA Film Fest on 6/9/14 in 3D with the director and America there in person.
While I am a "fanboy" of the original, I do think there's enough objective quality that anyone can recognize the dialog, acting, music, animation, character design (aside from Hiccup, darn it) were all higher quality than most would expect from a kid's film. In fact, I think it's quite nearly Pixar quality.
My expectations for HTTYD 2 were understandably high, but at the very least I just wanted it to be AS GOOD as the first.
Unfortunately, that's not the case so please adjust your expectations accordingly.
PROS:

Even better animation, textures, and epic, awe-inspiring scale

Same lovable characters, appropriately aged

Toothless being Toothless

Stunning 3D

Solid acting (except for Jay)

More great dragons

SOME beautiful scenes/moments (not enough compared to original)

CONS:

Messy pacing. Big things happen with little suspense or anticipation...sabotaging the drama and satisfaction of those scenes.

Dialog can be cringe-inducingly cheesy.

Main villain is barely even a character he's so undeveloped.

Jay's acting (just wait for his last line)

Overall, it lacks the depth, refinement, dialog, and compelling pacing of the original. BUT, it's not a "bad movie"! It's head-and-shoulders above most kids films, but compared to the first one...it is a step down. Still very enjoyable and definitely not terrible - just don't expect the first one.