High☆Speed!: Free! Starting Days is a solid movie that will likely be enjoyable to fans of the TV anime, and potentially even those unfamiliar to the franchise as a standalone coming-of-age film.
The story, while nothing exceptional, is solid. There is a degree of repetitiveness among the two seasons of the anime and this movie in terms of main themes and sources of conflict, and if this movie's other elements weren't so well-done I wouldn't have enjoyed it as much as I did. Fortunately, that's not the case. The movie had uncertainty about the future, family drama, and, as this is Free!, friendship being its main drivers, and while it did get a bit too melodramatic sometimes, overall I feel that the story was handled well and made for a movie that had some substance instead of having it be an hour of fanservice, which was a route they could have easily gone down.
There are some moments in the film that feel a bit awkward or shoehorned in (for example, Sousuke had more interaction with the gang than I'd previously thought from the way they act towards each other in the future, and I did question Haruka's future attitude towards competing.) but I don't think they detracted from my enjoyment of the film in a major way.
Where I feel this movie did an exceptional job is its characters. I was worried, at first, with such a large number of the main cast (especially since there is already an established universe) being original characters (not counting the novels). I was pleasantly surprised that all of them received some amount of development and had good, believable dynamics with each other. Overall, both new and familiar characters were likeable in their own ways, and I found myself emotionally invested in them.
One other thing that the movie did excellently is developing the relationship between Makoto and Haruka. For characters whose relationship in the future is already so well-known, their interaction in the movie never felt unimportant and are, in fact, what I believe are some of the strongest points of the movie, whether or not the larger franchise is considered. I left the theatre with a greater appreciation of their friendship, and I believe a better understanding of the relationship between the characters' older selves.
This being a KyoAni production, it was definitely a visual treat. While
I do think their style can be rather bland, the movie is undeniably very pretty, with fluid animation, great backgrounds, and good use of colour when it counts. There is one particular scene between Makoto and Haruka that was animated beautifully (more so than the rest if the film,) which I feel really emphasised it as a pivotal moment.
The sound and music were also fine, and served their purpose well. The music will sound familiar to those who have seen the series. It's not a soundtrack that will merit multiple replays on its own, but it was definitely effective in the context of the movie.
Overall, this is a movie I can recommend without reservations to a fan of the series. While I can see how it might be less interesting to someone not already interested in Free!, I think it still merits a watch for anyone who wants to see a beautifully animated but sometimes slow-moving coming-of-age film.
Note: I saw this movie in Japanese with no English subtitles. I am currently a Japanese language student, and while I'm confident that I understood almost everything in the movie, there may have been some things I missed. I will update this review if my opinions change after I see it again once the DVD comes out.