So I watched the movie yesterday, and I thought I'd just share my opinion here
I try to make it as spoiler-free as possible, but I can't promise anything
I've already read critiques before watching, and for most parts, I agree with what has been said, both positive and negative remarks. The movie didn't disappoint me but it didn't suprass all my expectations either. One aspect that the movie excels in is crafting a story that is engaging for both Vocaloid and Project Sekai fans. It took place in the Project Sekai setting but there were a ton of hidden references that someone who's just playing the game wouldn't have noticed. On the other side if you aren't familar with pjsekai the amount of characters was most likely overwhelming. Since a movie is tied to a time limit there wasn't really much time to dive into anyone's backstory, especially since it was Miku-centered, so I can forgive that. They even had a quite good solution but I won't dive deeper in that because I try to keep it spoiler-free.
This has been mentioned in this thread before, but there were a ton of already existing Miku songs, which was a detail I loved. As for the original soundtrack, I was disappointed. Yes, I've listened to the songs beforehand, and yes, I know they probably wanted to play it safe, but aside from the ending and maybe the Leo/Need one every other song is pretty forgettable imo. This saddens me because I do know that there are popular Project Sekai commissions that are much more memorable, such as Lower One's Eyes, Cinema, Beat Eater etc.
Aside from the story which was really cool I also liked the overall animation and atmosphere of the movie a lot. It just felt very warm and welcoming especially with all the references and how much detail some of the scenaries had. I also love that when the characters has conversation the camera angle made it seem like you're a fifth member listen to your friends talk.
Overall rating: 7.5/10