The story and the message behind Frozen 2 is excellent, but the execution make Frozen 2 somewhat too difficult to understand for young children, and overly lackluster for adults.
Walking into Frozen 2 with expectations for another mega hit like "let it go" will certainly be a "let you down". The idea of exploring your purpose, changes in life, and correctly wrongs from our precious generation is all great on paper, but it may be too ambitious for the Frozen franchise since the film and especially its toys needed to cater to young audience. With Mickey pulling the strings on the business side of things, it is very hard for the storyteller, the director, to balance between pleasing the young fans and telling something with deeper meaning. In the end, the end product is something that tries to shove things like Kristoff's boy-band singing scene, the overly early revealing of Elsa and Anna's parents and grandparents roles in the story.
Frozen was a huge success because of the lack of burden from fans and sales. Ironically, the inability to let the popularity go led to a sequel that felt like it was heavily weighted down.