I also rather enjoyed. The performances are very good and the casting was inspired. As with the book, if you were paying attention to politics in 2008, there's not a huge amount of new information here, but what is new is quite fascinating.
The Palin we see in "Game Change" is at different times sympathetic, pitiful, and horrifying. We see her thrown into a high stakes game for which she was terribly unprepared. We could fault her for that, but how many of us would refuse the offer she was given? Imagine being told, "There's an American hero running for president, and we think you could help him win, and if you don't, a terrible person will end up getting elected." Even without all the fame and fortune being implicitly offered, that's still a tough thing to walk away from. But then we see her come very close to (or perhaps even have) a mental break. The film is somewhat voyeuristic in this way. No, politics ain't beanbag, but it's uncomfortable seeing it destroy a person. The campaign and Palin's family seem to help her through the rough spots, but to the point of overcompensation; by the film's end, she's an overconfident monster who believes that the rules and history do not apply to her.
Although we don't know exactly who provided the background information for the book and film, it seems highly informed by consultants with a strong loyalty to John McCain. While Julianne Moore's Palin is a reckless diva, Ed Harris' McCain is a potty-mouthed saint. He grows uncomfortable with the "dark side" of populism and often steers the campaign away from less savory tactics. He wants to win, but to do so responsibly.
And that's where the film became troubling for me. It goes out of its way to depict McCain as a principled man who would rather lose with dignity than win ugly, but if that's the case, how did he end up picking Palin? For a septuagenarian with a history of cancer to pick a grotesquely underqualified vice presidential candidate is manifestly irresponsible, and he did it for the sole reason of increasing his chances of victory. Arguably, that's a lot worse than running a race-baiting ad for a few days.