I don't want to spoil the movie for anyone, but there are a lot of things that ended in a really unsatisfying way or were just sorta dropped halfway through. It started fine. Hiccup and Toothless develop a fun father/teenaged-son dynamic once Thotless enters the picture. Berk is dangerously overpopulated with dragons thanks to Hiccup fostering every dragon he rescues from trappers. The villain is a chessmaster dragon hunter who is always 100 moves ahead of the hero's and also he fucking loves his job and is a huge nerd about it. Unfortumately the hidden world plot points kinda steam roll all that and what was left felt poorly justified and/or unearned which became more frustrating as the movie progressed and ultimately built up to a really lame conclusion. I left feeling like there is fantastic movie berried not too far under the surface of this pile, but what we got instead was a mess and I'm not sure why or how it ended up that way.
Anyway, have a Thotless.