Just saw The Maze Runner, and let me say that it was fantastic! Last July I picked up the book because I saw something about it on Pinterest when I was looking up stuff about Ender's Game. I was ecstatic to find out after a couple days of diving in that a film based on it was going to be produced. Enough of the small talk though. *Unabashedly sings "Lets Get Down To Business" from Mulan* I know why you're here.
In terms of difference, there was only one major misrepresented concept. The griever hole. The way it looked, was found, and operated wasn't the same as it was in the text. Not to say that those scenes weren't still cool, but I am a sucker for following books (you really can't get any better than that).
Anything else that was different was in terms of practicality (appearance of characters, communication, places, and transportation).
Aside from those mandatory movie changes though, the only other major downfall I experienced during the viewing was the amount of language (one thing I liked about the book was that that element was far and few). There was quite a lot in the first part, not so much in the middle, and then a little more in the end.
Overall though, I would say that the good outways the bad. For the most part, it's a clean, family-friendly movie that stays pretty true to its origin. So shut your devices down, go out, and see what I'm talking about!