Spoilers below.
The plot takes some creative licenses to force drama that are hard to forgive. The main male character is selectively an amnesiac to increase drama in a way that can feel cheap and unnecessary, especially when he loses memory of the name immediately after repeating it over and over. Somehow in the entirety of his experience, he never once had the year or the name of the town mentioned to him, nor did the girl, otherwise the big reveal would already be known to them. The grandmother is randomly and ineffectively revealed to be a baba-yaga style all knowing sage, which just makes the plot seem cheesy at that point.
Most importantly, though, is just that the entire meteor portion of the plot could have been cut and you would probably be left with a better story. Simply have the phenomena suddenly stop after the celestial event with no disaster, and proceed to have a missed-connections theme like Shinkai Makoto's other major movie, 5 Centimeters per Second.
Which leads into the last major flaw: Makoto's apparently petrifying fear of writing actual relationships. We saw a smidgeon of one in 5 Centimeters, but he damn well makes sure not to include much actual interaction within the romance, preferring to instead show the angst of love "forgotten". Perhaps this is what causes him to love the "missed connections (AND TRAINS)" trope so much, which at this point is becoming more of a detriment than a strength to his films.
All in all, the gorgeous animation and sound, as well as an interesting initial premise, still made it a enjoyable watch for me despite my gripes with the plot. I enjoyed it more than 5 Centimeters, which I gave a 7, so I'll give this one an 8.
