Let's get to the important stuff first: As Sarah Palin, in the new HBO film Game Change based on Mark Halperin and John Heilemann's bestselling behind-the-scenes book about the 2008 presidential election, Julianne Moore winningly captures the physicality of the Thrilla from Wasilla. (The film premieres on HBO Saturday at 9 p.m.) Yes Daniel Orlandi's costumes and Ardis Cohen's hairstyling are dead-on accurate, but also Moore successfully mimics Palin's odd jerkiness of movement, the small stiffness that caused some of her detractors to call her robotic. Moore is less successful in the accent department (accents are not her forte — for further proof see her Mayor Quimby impression on 30 Rock), but even with that there are moments when she comes frighteningly close to the real-deal. All told, it's a mesmerizing, breakneck performance, one that elicits equal parts loathing and sympathy. Moore has always been excellent at projecting tightly wound but ever-rattling anxiety, and through that lens a fascinating portrait of Palin as an epically tragic figure emerges. Here is not just the guileful striver we've seen in dozens of Fox News pundit sessions, but also the tenacious family woman, the hungry and curious small-towner, the deceptively self-conscious good girl quietly roiling with an unnamed darkness. It's a captivating piece of work, akin to Laura Dern's bonkers Katherine Harris in director Jay Roach's other HBO political docu-drama, Recount.

It's a shame, then, that the rest of the movie is so much flatter. While Game Change the book dealt with a much wider expanse of the electoral landscape, the movie is chiefly concerned with the ballsy, and perhaps ultimately disastrous, decision to bring an unknown, untested way-Northerner into the white hot center of a presidential campaign. So we're mostly dealing with Moore as Palin, a disappointingly miscast Ed Harris as John McCain (was Michael Hogan unavailable?), and Woody Harrelson as beleaguered campaign advisor Steve Schmidt. Though, really, we don't see all that much of McCain, and what we do rather ludicrously exonerates him of any wrongdoing in the whole debacle. McCain's increasingly desperate antics, his at-all-costs drive to win that fatally sunk his reputation, are nowhere to be seen in this film. He's painted as a bit clueless, sure, but his many scenes of steely resolve to "not run that kind of campaign" are never balanced out by anything resembling curdling ambition or even complicity. There are a couple of small scenes that aptly show McCain struggling meekly against the wave of populist anti-Obama outrage that tainted the campaign late on, but that's about the only genuine insight into the man that was almost president. The rest is a kind bit of whitewashing, perhaps even a mea culpa from the very media that movie McCain accuses of betrayal.

The film is swift, brusque, and near-fatally expository. It's factual and straightforward in a way that feels lecturing and textbook, like Sorkin on his bad days. (Even the people in the cheap seats know we're "living in an age of Facebook." You don't need to summarize the culture for us, thank you.) Danny Strong's adaptation admirably hits the important beats, when it comes to the timeline at least, but on occasion there are lines that seem far too theatrical, too ginned-up and movie-ready. I suppose the filmmakers had to find some way to make the recent past exciting, lest the whole movie seem merely like an especially expensive courtroom reenactment, but for a film that's largely going for you-are-there realness, the linguistic flourishes do no favors. Like, did Sarah Palin really lean in to Steve Schmidt and say, "We have to win. I so don't want to go back to Alaska"? Maybe she did, but in the film that line and several others are sore thumbs, indications of an only half-successfully repressed desire to sensationalize.

But, of course, it ultimately all comes back around to Ms. Palin. As a two-hour-long psychological profile, ultimately glancing as it may be, Game Change is more than interesting. Moore never goes for caricature or sketch comedy, she leaves that to the capable Tina Fey. No, this here is a marvelous, fully realized creature. A creation so strange and scary that it would seem like a cartoon, like something dreamed up by a fabulist, if it weren't, of course, so real.