These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Five Centimeters Per Second
Epileptic Trees: Due to the nature of the ending, this movie invites Epileptic Trees with regards to the future of its characters. At this point it becomes notable that, contrary to his reputation, Makoto Shinkai has never actually made a movie with a genuine Downer Ending. Voices of a Distant Star and The Place Promised In Our Early Days both worked out in the end—but then, neither of those movies were set in the 'real' world.
In Love with Love: Takaki. No doubt he really did care about Akari, but as he grows up and they drift apart, it would make one wonder if he would still feel the same way if they ever meet face-to-face as adults after not seeing each other for so long and having virtually no contact.
Needs More Love: A larger fandom might cathartise some of the feelings that this movie invokes in people.
Wishful Projection: Seeing that most of the film is from his point of view, Takaki might not have actually seen Akari at the end of the film and it could have been a figment of his imagination due to him never being able to move past being separated from her and not knowing how to cope with it in a proper, healthy way - at least not until the very end where it is implied that he realizes that he needs to do those things, to grow up, and to come to terms with his past.
Not to mention, she did disappear a little too quick (N.B. this is probably Shinkai's most realistic film, after all). Although yes, she would be a good distance away from the railway tracks once the train has passed, Takaki would still be able to see her walking from where he is standing. Plus, trains that carry passengers go by much faster than cargo trains which would give Takaki enough time to be able to see her walking away once the train's passed, if she actually was there.
