This "movie" is 100% for the fans of the show. As I am just a causal viewer and not a fan, it was not for me. To me it wasn't even a movie, but a retelling of the story with some conflict in between. The first part of the movie was telling the whole story of the Universe, which I get for people that don't know the show.
Then conflict happens and now the main characters lost their memory. How do you get it back? By regaining the lost memories, ie: retelling the story.
The music was very forgettable for me, and almost all sounded the same. The villain was so out in left field compared to the rest of the cast that it made me feel that the creator just played a few to many hours of Bendy or Cup Head and said "I want that."
To me this did not add anything to the story arch or character developments from the series and could have been easily another episode if all the backstory retelling was cut out.
For how much CN advertised this I was curious about it. I watched the whole thing cause I just really wanted to know what is up with the Spinel character, but in the end I felt it was a giant waste of time.