I did think they tried to cram a little too much into ~90m however. Certain series of events felt rushed and certain aspects of the story glossed over or a bit threadbare (Stoick's death and Hiccup seeming completely oblivious to the Alpha's ability to control other dragons and thus overreacting to Toothless stands out to me) but they're minor complaints overall.
I loved how it escalated the scale of the HTTYD universe with other humans, other viking clans, more dragons, more sky/land/water, more 'period' technology and culture. It even raised some questions about the universe that I think could make some interesting further films: Toothless as the last Nightfury, Hiccup/Astrid (and mom? I think the lines she drew on the ground were supposed to expand Hiccup's map) mapping the world, Hiccup as Chief and Toothless as Alpha and how that strains their relationship/unites the species, subsequent challengers to Toothless as Alpha, Hiccup/Astrid falling in love could even make for a classic Disney-esque story.