This movie in one word: Brilliant.
But I may be a bit biased here. I love dragons. Please read my Maleficent entry for proof.
That's the plot trigger. Hiccup embarks on a peacekeeping talk with a guy named Drago who wears dragon skin as a fashion statement and screams bloody murder to control dragons. Come on! Who would want to chat with a guy like that?! But Hiccup was never one to listen to reason, and so the story goes on.
Hiccup's mom has issues. What keeps her going is her life-long mission to protect dragons, which makes her abandon her family in the process. Okay, so now we know what her priorities are. It's like the modern day working mom choosing her career over her loved ones. But, heck, she's the Dragon Master! If I had a job as cool as hers, I'd rock the family tree.
Have I told you I loved dragons? Toothless just pushed that adoration a hundred knots higher! That part where the minute Night Fury challenged the Alpha Dragon whose like as huge as a couple of Mount Everests was just… just… intense! *swoon… slow clap… sniff*
(Yes, animated films make me more emotional than live action films. Sue me.)
Poignant to death, the film shattered my heart when Toothless accidentally kills Stoick with his laser blast brought on by mind control. Seriously mangled my heart there. Hiccup finally has his family together and then this happens. Aaaah… my poor, poor heart...
But the high point for me was the mutiny of dragons in the end. Nothing rocks my joes quite like a scaly, fiery uprising. And when Toothless was hailed the new Alpha, man, goosebumps! I got more giddy about that sequence than Hiccup being crowned the new Chief of Berk. (I like dragons more than I do humans. Sue me.)
PS. Personal cringe moment for me: Hiccup looks weird as an adult. Puberty wasn't kind to him. :)