Prepare yourselves, this is a long one. I spent too much time thinking about a kid's movie.
I'm going to be honest, I don't understand the love for this movie. I know I've given it a high rating, but that's because this entire trilogy means a lot to me personally. However, this is easily the weakest film in the trilogy for me. The story never really gets to hit its stride the way it does in the first because there are too many plot significant events happening at the same time. This makes the themes and messages of the movie weak at best and contradictory at worst.

Drago is an interesting villain in concept, being a character that Hiccup will not be able to change, but in practice it just made him a generic Sir Villain McBadguy with nothing interesting about him other than his intimidating screams that somehow manage to [spoiler] control even Leviathan class dragons [/spoiler].

Toothless. Look how they massacred my boy. The intelligent, curious creature I fell in love with has been replaced with a cute mascot with no personality of his own save for like 2 four second scenes. He acts in such a goofy, doglike manner all the time that it made 14 year old me (at the time) cringe. He's domesticated, I get that, but even when he [spoiler] KILLS HIS FRIEND'S FATHER [/spoiler] there is no introspection on his part. Just Hiccup telling him it wasn't his fault and moving on like nothing happened. Why was it Toothless who did it if the writers weren't going to do anything with it? Luckily they returned him to form later in the third movie but that does not rectify the issues here.

[spoiler] Meanwhile we have the whole thing with Hiccup's parents, and I for the life of me cannot understand the purpose of Hiccup's mother. She does not aid in Hiccup's character development at all. She basically acts as an explanation as to why Hiccup is the way he is (which no one asked for) and someone Hiccup can relate to when he's separated from everyone else. The most significant function she serves is to made Stoik's death more impactful, as he finds his love again as a changed person only to die quickly afterward. Not that that's emphasized, this movie can't choose a character to focus on and as a result I can't feel for any of them.

So, let's talk about Hiccup. Hiccup's character arc in summary goes as follows: "I like exploring and don't want to be chief, I want to be a peacekeeper." Later: "Man, the world does not want me to be a peacekeeper or explorer, better do what my parents want me to and just protect my own." This is even expanded upon in the third movie when he has to abandon all the dragons for the sake of not being hunted all the time. I like the idea of him having to accept that's he's going to be Chief, but I think breaking all of his ideals is a bit much, although potentially realistic in a sense. [/spoiler]

TL;DR: Not great but still a solid movie.