Ender's Game the movie was to Ender's Game like Circus's forum icon is to Circus. Ender doesn't have feelings in the movie, he is a child robot that wins at zero space vidya games because he is the chosen one. When he isn't being fanboy'd endlessly in the movie by Harrison Ford who might as well have a huge erection sporting every time he looks at Ender because his mouth is always open in anticipation of being violated by his underage ****, we are given Ender who might as well have been acted by a thirteen year old Keeanu Reeves playing the role of a thirteen year old Neo who is getting trained to kung-fu foreign aliens to their death.
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There is one event in the book where Ender breaches his isolation from the other students by gradually forming a relationship with someone else who is part of an 'Ender-hate faction.' Ender intentionally takes steps to make sure they can talk and develops an actual close relationship with them resulting in him being able to connect with the rest of his classmates. Take a note that there explicitly is no 'Ender-hate faction.' Rather a social-psychological phenomenon where Ender accidentally breaks the arm of another cadet named Bernard after he continually pesters Ender. Bernard gets pitied and uses that pity as leverage to extend his own influence which is permeated with anti-Ender sentiment. Coupling this with Gaff (his commander) isolating him on the shuttle to school by highlighting him as being special leads to his intellect being an ostracizing element. Despite this, Ender's intellect enables him to make social relationships despite the barriers Gaff constantly erects. Gaff does this in order to forge Ender to rely only on himself on finding solutions because he is being groomed to be the definitive commander.
The beginning of the book is largely framed by psychological conflict and side questioning. One which proceeds throughout the book is that Ender can never figure out Gaff and it is a source of intense questioning within the book whether Gaff can be considered a friend. In the movie, Gaff is Harrison Ford.
Ender's game isn't about the results, it's about the methods and the means. The depth from that analysis is similar to an ideal mafia game. Mostly discerning motives of the players, how their trending opinions will develop, and in order to achieve your own objectives what is necessary in order to be accomplished. Ender does get tired of the game. When Bonzo Madrid assaults him in the showers he takes defensive action to fend him off. In the book, Ender begins to despite the system that creates the malicious attitude that Bonzo sported. He doesn't fault Bonzo himself but rather the education at battle school that 'created' someone to become 'Bonzo' or put someone like Bonzo in a position of high responsibility when it should have been obvious that such a commander would not be effective in actual combat. In the movie, Bonzo's brain is on display and a mechanical arm robot is doing surgery on him. Ender gets upset. The audience is left to assume that this is a discourse of the cost of war. Harrison Ford is called a monster, but yet again we don't know what Ender thinks. We are just left to our own musings of how bad he is treated and that our pity is analogous to his own emotional pattern (it's not).
The lack of having a personal insight into Ender makes the movie lifeless and mechanical. When Ender expresses emotions it is a 'duh' moment precisely because Hollywood took short cuts in making this big screen. In utilizing Petra, she is abstracted from being a fierce self-advocate to being a tom-boy love interest. Why. She is the only female cadet really mentioned in any detail in the book therefore making her the only heterosexual love interest Ender could develop if she was even into that type of thing.