Lacks the originality and charm of its predecessor.

Rating: 6/10 (21 October 2018)

This sequel is a huge disappointment. The main problem lies with the narrative. While the original endeared viewers by eschewing the obvious and common narrative of good-versus-evil, encouraging people to be more understanding of others and finding nonviolent solutions to longstanding conflicts, the sequel instead revels in violence both to establish the plot and resolve the final conflict.
To quench any moral qualms a viewer might have after internalizing the message of the first movie, the second one focuses its action on a suitably hateable, mean-looking, rough-sounding cardboard cut-out of a villain (boringly named Drago) that wears his intent to dominate and destroy on his sleeve.
Visually, the movie looks just as stunning as its predecessor, but often the visuals don't match the narrative, as if there was little coordination between the script writers and the animation team. For example, the movie opens with a beautiful overhead shot of the gorgeous Viking settlement, Berk. "It may not look like much", Hiccup's voice-over comments without sarcasm. Doesn't look like much, really? Are we watching the same scene?
More serious is the disconnect between narrative and visuals in the depiction of violence. In the movie's second act, two major characters (one dragon, one human) die violently in battle, but without any trace of blood. In fact, despite the extensive battle scenes, there are no visible injuries of any kind in this movie (excepting a broken tusk, and of course some fully-healed stumps). I understand that this is supposed to be a kid's movie, so obviously the animators didn't want to go all-out on the blood and gore, but it also feels wrong to make violent conflict look so inconsequential. Again, there seems to be a disconnect between the writers, who play up the violence for dramatic reasons, and animators, who tone it down to avoid scaring the children.
The final confrontation between the villain's Alpha dragon and the hero's Toothless is similarly jarring. Visually, the Alpha looks like a hulking beast, thousands of times larger than any of the regular dragons, likely able to demolish Berk with a single charge. However, the plot dictates that Toothless will now defeat the Alpha, and thus this giant dragon does nothing but stand still and growl ineffectually. "Fiiiight!" the villain yells desperately, as he realizes his downfall approaches, and for once I sympathize.
All in all, How to Train Your Dragon 2 is not a terrible movie, but it's so unoriginal that it's basically interchangeable with any of DreamWorks second tier works.