Gbaji was saying that Ender is playing the game and the game just looks super-duper realistic so we get to see "space battles" occurring that are supposedly not occurring, except that they are. 3D holographic Starcraft and all that rather than what we think of as a military tactics simulator with dots and triangles and stuff.
The major issue I see with that (and with the preview) is that it sets your mind into thinking of it as an actual battle and not a "game". Which again sort of blows the whole point of the movie if you spend the whole time viewing it as actual battles. Maybe they'll spend significant time trying to impress "This isn't real!" while wanting to show off nifty space battle effects. I think that pulling back on that would make for a more faithful adaptation but, you know, Hollywood and all that.
I don't see why this is a problem. The only difference between what's portrayed in the film (previews) and in the book is the level of detail of the holographic images he's working with. From an objective point of view, there's no more reason to assume that these images must be portraying "real battles" anymore than the blips on a screen that were portrayed in the book. It will work in the film just as it worked in the book. Because, as you just said, he is told it's just another simulated war game. And just as in the book, the film will have contained a long series of such things up to that point, allowing the audience to accept it as true.
I expect that for the typical person watching this film who's never read the book, they'll get to that point in the film and think "Oh. Those space battles I saw in the previews were just simulated training", then when the reveal occurs, they'll be like "OMG!". Because that's exactly as it happened in the book. Remember that Ender (and the reader) is never told anything but that Ender is training to be the next generation of leader defending Earth from the assumed third invasion
. That's largely why the twist works. It has nothing to do with how much detail the holographic images contain.
Um... And let's be honest. Scenes of kids staring at moving dots on a screen wouldn't make for a very exciting film. So yeah... Hollywood. But I don't think it'll detract from the story one bit (assuming they don't screw it up with too much foreshadowing or something. I never underestimate the ability of Hollywood to dumb things down for the dumbest rock in the theater). It's a tricky set up, but if they do it even mostly right, it'll work. Like I said earlier, my bigger concern is getting the psychological stuff right. That's far far trickier than fooling the average viewer with a plot twist.