I won't see Ender's Game on principle. I may pirate it, but I won't financially support a property made by a homophobic bigot who uses his fame and influence to destroy the opportunities of others.
If you watched the first Thor/Captain America/Iron Man 2-3/Avengers and expected a decent plot and continuity then you deserve to be disappointed. That is like saying Pacific Rim was garbage because of it's plot. Today, movies like that spit on source material to appease the "bro" crowd with fancy images and hot women in tights. Ender's Game is no exception.
In the novel, the main character Ender (a tactical savant by age 6) is selected by an international fleet to defend the earth and the human race from extinction at the hands (or rather, claws) of the insectoid Formics, determined to colonize our world. The book covers his years of training, in which Ender is isolated from family and friends, pitted against fellow child geniuses, and manipulated by his superiors to take drastic and horrific actions without his knowledge, all in the name of the greater good. It’s an intense and stressful book to read.
The film has almost none of these elements. Characters are rewritten to seem silly (the depiction of Bean was a particular outrage), while others have changed dimensions that change the tone of the story. Far from isolated, Ender finds staunch friendship in fellow Battle School trainee Petra. In fact, their relationship worryingly contains overtones that could be construed as prepubescent beginnings of romance.
More devastating is the complete omission of several gut-punching revelations designed to unsettle the reader. By the time you finish the book, you are horrified not just by what the children are forced to do but by what murderous little monsters they seem to have become. None of this is included in the film, and instead we are left with an action-adventure film for teens with poor dialogue. While the cast is mostly very good, with few notable exceptions, they are left with clunky and often cheesy lines to deliver. The ending was given a completely different feel after so many little changes to mitigate the intensity of the novel.