I liked Ender's Game (mostly) until the end.

The only complaint I had was a sloppy/lazy timeline (unnecessarily including information that made it seem like events that took months according to the dialog happened in 28 days). Overall it was pretty close to the book until the end. They completely left the tracks with the ending. Pissed me off to no end.

Of course I say that having loved that book since I was about 12. I don't know if anything but an HBO/Showtime mini-series could have told that story in a way that met my expectations.