I'm going to compare this movie to Empire of the Sun, as they bear similarity, so spoilers for both
[spoiler] The main theme in both of these movies is; suffering. However, in GotF the suffering is mostly by choice. in EotS, Jamie does not choose to suffer and feel alone, he is thrust into a camp and the only choice he is given is to either further his suffering with the chance of reuniting with his parents, or join the pack of other westerners that will most likely lead him down a path of chaos. Seita chooses to isolate himself and his sister from his only living family simply because his aunt did not treat him well, and it ultimately lead to the death of him and his sister. He had a choice to suffer little, or suffer greatly, and he chose wrong. Both of these movies have a different outcome, yet somehow EotS had a more lingering presence in my mind despite the "happy" ending, because you knew he had no choice in enduring what he had to. GotF is still a visually remarkable movie with a dark and depressing story, however I feel as if the choices that Seita made impacted on my enjoyment of the movie. I understand he is only 14 years old and he felt like he could support himself and Setsuko, but everyone has a shitty aunt and if he had just stayed with her he may have survived. [/spoiler]

I recommend watching both of these movies close to each other to gain a perspective about both of them, as they are both movies that are great within their own merits.