let's be real: it wasn't good, there were good things about it but mostly it was just a mediocre and sometimes bad things
1.there was a large amount of cg, when uta is performing her movement is mostly similar to vocaloid mmd/concert tech. whenever it camera isn't close enough to have it be overly noticable it will switch to cg. lots of scenes of large movement was cg. though it makes sense because of the reclining animators, but credit to them because some of the fight scenes were animated beautifully.
2. the story writing is questionable at best, it wasn't exception, it was a typical shounen movie plot - some world ending thing happens but it is resolved by the power of friendship and love because its technically not canon and the characters have to be alive - and some parts don't make a lot of sense. many things were thrown in to make sense. the whole tot musica thing was made for the movie. it was another one of those overpowered things that could possibly end the world! oh no! well here comes the main character to save the day! and here the movie ends, and now you all paid money to see a mediocrely written plot of your favorite anime.
overall there is also things like severe fan service, like things happening so that it could be a good marketing placement, oppertunities for merch, etc.
but despite these, there are good things about it too, especially when you are a big fan, things like shanks showing up, the fights were extremely hype and so many throwbacks to the anime itself. these are all things that you can probably only enjoy if you are a big fan. things like the red hair crew and the mugiwara's fighting basically alongside each other, shanks showing up.
there's also the music, the music is absolutely beautiful, the vocal artist ado, who's been blowing up in japan in recent years with her voice. as someone who had listened to her for a while i was super happy that she was featured in the film. and if you like the music in the movie definitely listen to the full songs and just ado in general. the movie uses its music extremely well, the songwriting and placement was beautiful.
one of the songs, backlight, was featured in the movie - the animation that went with it, the scence itself, were so impactful and ado had so many amazing vocal cues in it. if you've listened some of her more popular songs you can see her style. i'm glad the directors let her have a song that fit her so well. it gives me goosebumps everytime.
this movie made me cry, not because it was bad just because no matter what cry bait you throw into the movie, oda still has the skill to make you care about the characters and be sad about them, the voice acting was as usual, amazing. kaori nazuka (who also played nunnally in code geass and a lot of roles, check her out) blew it out of the park with some of the scenes. all the other characters also did amazing. the emotion of the characters and some of the animation was so clear and so effective you can't help to just be sad.
in all, it wasn't that good, it's another piece of content that is used to make more money. but if you are a one piece fan, watch it, look past some things and its still amazing.