I read the book right after it came out. It was a very good book.
The bulk of the book was actually about the democratic candidates: Obama, Clinton, Edwards, with probably only 1/4 of the book being about McCain and Palin. Furthermore, at the time of the book's publication, the big revelations from it were about the Edwards
and, to a lesser extent, some intemperate remarks by Bill Clinton
and Harry Reid
. Conversely, by the time of publication, there was really no big surprise in learning that Palin was ill-prepared at the time she ran for VP. That was pretty clear from watching Katie Couric live as it happened.
In fact, the title of the book, "Game Change," was about Obama and the Clintons. Obama, widely seen as an underdog was able to "change the game," win the election and, ultimately, have Hillary Clinton work for him.
And, yet, from what I understand, the movie has none of that. Instead it was all about a minor--and well trod--part of the book.
Combine that with the fact the director is a democrat partisan
and, right or wrong, it would tend to make conservatives suspicious.