Spirits Within is like the first 10% and last 10% and somewhere in the middle 10% of a Final Fantasy slapped together as a movie. Final Fantasy as storytelling isn't really translatable to the big screen, you have one and a half to two and a half hours to fit material into for most movies, and a Final Fantasy movie would need like several times that at least lol to fit in all the character and plot points. If you strip it down it fails, like Spirits Within. Maybe a trilogy could pull it off, but the basic framework of Final Fantasy stories is there's a big twist or raising of the stakes halfwayish through, which is fine for a duology but tricky to split that kind of story into a trilogy. Final Fantasy is a story the audience is intended to unfold over multiple days or weeks or months playing vidya, not through a few hours in a movie theater
As its own thing Spirits Within wouldn't be completely terrible, but it's not Final Fantasy. It's a few generic details from Final Fantasy slapped on to a not-Final Fantasy