@coin Things that have changed are the gates themselves and going from one point of view to an ensemble. So for example the third gate in the movie, but imagine it as Wade playing the main character of War Games, or playing as a live action version of a video game character in character. Finding the gates was different as well; finding the third one involved Rush's 2012.
As I said earlier, a lot had to be changed because of rights I suspect, as a good deal of things are now Warner Brothers references, or Spielberg references. They added a lot in though. The other major reason would be of course the VR aspect of it all. Not only was the book a PoV of one character so you got his thoughts, but because of VR the reader actually could see through the character's eyes were seeing it.
Same plot but definitely an adaptation but enough to make them each stand out as their own thing. But if you go from one to the other expecting things to be the same, you will be disappointed.