We saw over 150 movies this year (2013), so many that I'm sure I missed reviewing quite a few, like Ender's Game. We saw it second run and The Boy liked it. I also liked it, just not very much.
There was a dumb controversy surrounding it because sci-fi icon Orson Scott Card apparently said something (about gay marriage?) that was not approved of by the bien pensants, who apparently lack the sort of nuance that all those who disagree with them must embrace if they wish to partake in the modern culture at all.
To wit: You suck, but that's a pretty good song/movie/book.
The movie is essentially a standard young-adult space opera, as Heinlein might've written in the '50s, about an Earth that has barely survived an attack by evil ant-aliens (or was it bees?) and has rebounded by embracing a militaristic society where children are trained from a very young age to defend against an expected future assault.
It isn't well explained, but basically only the young have the adaptability to defeat the Alien Menace. (This gives it both that young-adult feel I was mentioning and an unfortunate Harry Potter vibe.)
Our movie shows Ender's progress in and out of the academy (which is highly manipulative), in boot camp, and in training for the anticipated future battle, and is fairly unobjectionable in its particulars.
I would single out Harrison Ford as being particularly miscast as a long-time military dude, but then I began to realize that I didn't think the possibly flawless Viola Davis was very good either. I've forgotten the kid (Asa Butterfield, Boy In the Striped Pajamas). His older brother seemed awkward and even Abigail Breslin as his older sister didn't feel quite right.
Nothing seems to fit here. There are all these little vignettes: Zero-G combat training (which never comes up outside of training), Ender's conflicts with his peers, his emergence as a sort-of leader, a mythical and possibly dead hero but something's up with the whole story, the sexual tension he has with a girl (Hailee Steinfeld, True Grit), and on and on.
Nothing seems to gel.
The movie's both too long and too short, if that makes sense: It's too long to be a fun, fluffy popcorn flick, and too short to develop all the critical mass it needs to carry its desired dramatic weight. This probably comes from not wanting to cut key elements of the 384-page book down even more than necessary but being stuck with having two hours to cram the whole thing in.
I mean, if you're Peter Jackson, you make it into a twelve-hour movie and add a sub-plot about ants in love. But if you're Gavin Hood (Tsotsi) you probably don't have that luxury. Might be worth viewing an extended/director's cut.
The Boy, as I said, liked it more than I did. And even though I've been critical, I wouldn't say it was bad. It just didn't work very well somehow, at least not for me.