I had a lot of hope going into this one and was thoroughly disappointed.
The movie had very fun character designs and a beautiful, colorful world. The character concepts were fun and interesting, as was the initial concept of the movie. I was excited to watch this with the concept of two parents turned into monsters slowly remembering themselves on a grand adventure, and although I was surprised by the songs, I didn't mind them. They were overall fun, and while not the most amazing songs in the world, I liked them.
However, as the movie went on, I was more and more disappointed. The pacing was a bit off, but that was minor. The plot was a little disjointed and nonsensical, but it is a kids movie. However (spoilers), the "twist" of them getting divorced was poorly done, to put it mildly. The parents' fighting throughgout the story was a little cliche and unsatisfying. Throughout the whole movie, the two put undo burden on their daught, somehow only getting worse as they return to themselves. When they realize they were about to get a divorce, they spring it on her in the worst way possible, and her subsequent breakdown (although completely understandable from the perspective of a child who's been doing the work of ten adults and was never acknowledged) was framed as her being unreasonable.
The movie did end in a good place, but that to me just didn't make up for the incredibly unhealthy portrayal up to that point, with a combined message of "don't feel bad feelings even though everything is going wrong and hurting you." As someone with divorced parents, I am glad that this is being addressed in kids movies, I just wish it was handled better.