This is a movie that heavily relies on nostalgia to force the viewer to enjoy the film. There are literally thousands of references to movies, games, etc. from the past, with little to no future pop-culture references. If this movie takes place in the future, why is everyone so fixated on the late 1900s?

Nostalgia aside, the story is quite average and predictable. There are no real surprises or awe-inspiring moments.

Edit: I've just finished reading the book, which gave much better insight about the nostalgic focus, and it fleshed out the world significantly better. I think the movie's changes to the challenges weren't bad. I understood making the film's focus on action rather than mental puzzles, with less focus on actually playing through the old games and movies. It was more cinematic that way. The movie's biggest failure was that it didn't convey just how massive the game was and why it was so hard to solve the clues. Plus the Sixers seemed way more ruthless and unfair in the book, which made the book's final battle have much higher stakes and way more exciting than the movie's climax.