The Go-Touban series has always focused more on the sisters and their relationships with each other than it ever does with the actual romance plots. Each of the girls has gotten sufficient development over the series (although some are better developed than others), and that's still the movie's main focus and where it excels.
However, this had no right being over 2 hours long - a sign of poor planning and shoddy editing. Additionally, the animation & art, while colourful, is somewhat lacking for a movie production and ends up looking incredibly mediocre.
The sound design & soundtrack, however, are reasonably satisfactory, and the VAS have yet again done a great job at handling their individual performances.
It's a satisfying and tender conclusion to the series, but one that is otherwise overlong and bland.