I've posted a
full-length review of the film, but a few brief thoughts...
It would almost impossible to live up to "5 CM" - the first 25 minutes of which are IMO the most perfect film animation of all-time. And while this doesn't, it's still very, very good. Visually, of course, it's absolutely stunning. Shinkai remains an artist and animator of staggering talent. He also has a poet's soul, and one gets the feeling that every film he makes is a look inside that soul. Not just the beauty of the eye, but the elemental loneliness and longing of the characters.
For all that, I think the reason this film isn't a masterpiece is because it's Shinkai's most prosaic film, and poetry suits him better. He's not as good with big plots and keeping all the plates spinning as he is with very small, simple and pure stories. The feelings at the heart of this one are pure, but they're buried under too much polish and construction.