I'll say this as an avid pretty rhythm fan: If you don't watch Pretty Rhythm, Rainbow Live NONE of the characters,the idol world, or plot will make sense to you because this movie takes place after it. There are 3 Pretty Rhythm series out there. Chronologically, they start with PR Aurora Dream, PR Dear my Future, and finally PR Rainbow Live. Rainbow Live is in an alternate setting with new characters while Dear my Future is the (trashy) sequel to Aurora Dream. They are all idol anime for younger girls based off of a rhythm game in arcades and follow various "prism stars" in theirstruggle to become better. If you want to fully understand this movie, I'd say start with PR Aurora Dream (you don't have to but you will understand how prism shows work more if you do), skip Dear my Future because it's awful, then you MUST watch PR Rainbow Live.

Story
I personally really like the story. All of the other PR series focus on the girls side of things and its nice to finally see what some of the guys are up to. It starts by adding in some new characters as idols in Edel Rose and tells what Over the Rainbow has done after their debut. You follow along Shin, a new student at Edel Rose, as he learns how to do prism shows. The story has a few layers: the rivalry between Edel Rose and Schwarz Rose, Shin and Louis'(the guy that got Shin into prism shows) relationship and growth in the idol world, the King of Prism tournament, and leftover saltiness from characters that previously entered the King of Prism tournament. The story is still pretty easy to follow and interesting if you know whats up. However, a major flaw to this movie is that it doesn't complete the story at all and you'd have to watch King of Prism: Pride the Hero to complete the story. It also doesn't really feel like the story takes itself seriously because everything is so rushed, forced, and how absurd other parts of the movie are.

Art
The art is somewhere between average to bad depending on what your standards are. The normal art is ok. All the characters are pretty colorful and unique which helps in identifying them later since there are a lot of them. there is only one or two character designs I'd say I dislike. I said "normal" art earlier because the prism show use everyone's worst nightmare: CG animation. I personally don't mind it and I think it's better than the alternative of having really limited movement in shows because the shows are important to the movie. I will admit that they do go overboard with the sparkles and some of the special moves but it's good for a laugh. Also, some of the costumes these guys wear look absolutely hilarious.

Sound
Since this is a idol anime, there is a lot of singing. The music is ok and the lyrics can be kinda cringey/ corny but its not that bad. One of the guys is a trap and sounds like a girl but ¯\_(ツ)_/¯. Otherwise audio is all around ok.

Character
Some of the characters are from Rainbow live and there are at least 10 new ones, making for a LOT of characters to wrap your head around. Luckily, you can probably just remember most of the new ones by hair color and the only new characters that will really matter at the end are Shin and Louis. You do get some character development from Shin but otherwise it mostly just sets up character development for the future. The plot more focuses on the tension between Edel Rose's owner and Schwarz Rose's owner.

Enjoyment/Overall
As a Pretty Rhythm fan, I absolutely adored this continuation of the story while it does have flaws. I really loved that I got to see more male prism stars instead of the girls as usual. I feel like this and Pride the Hero will nicely tie up some loose threads left after Rainbow Live. It makes me kinda sad to see that this got such a low rating, i think at least a 7 to a 7.5 would be more fair. That's why I was compelled to write this review(this is my first one lol). I hope this review was helpful!

TLDR: Watch Rainbow Live first to watch this movie and fully understand it. The movie itself is pretty good if you are into male idol anime and are ok with it being more of a prequel to the next movie. Otherwise, I see a lot of comments that it's cringey because of the CG and the cheesy special moves during the dancing.