When books are adapted into movies, I think it's best to look at them as two separate works of art rather than comparing them. It's very difficult to translate one art form into another without making changes. Most novels of any length would require a movie of several hours for a literal transfer.
Ready Player One's movie version has the same basic premise, same characters, and to my surprise, the same messages. Having Ernest Cline cowrite the script was definitely a good move in that regard, a way to preserve the essence of the book in the midst of a remarkable number of changes. Major events in the book are often omitted from the movie. New events are added, and order of events is often different. Despite that, I had a lot of the same reactions to the movie as I did to the book.
The movie is a visual feast, but it also does a great job of addressing issues like the danger posed by corporate greed and the need for balance in one's life.
The movie appeals to the nerd in all of us in much the same way the book did, though interestingly a lot of the pop culture references have been swapped for others, I assume in some cases because of rights issues.
The relationship between Wade and Samantha is well handled. There is also an implicit comment on the problems of relationships that exist only online.
The movie is not without its flaws--no human product. That said, the good qualities far outweigh those flaws.