It was easy to figure out why the critics would hate Child 44, what with its depiction of life in the USSR under Stalin.
Spoilers: Life under Stalin wasn't great.
In fact, Child 44 shows us starvation, orphans, war, summary executions of parents in front of their children, torture, rampant politics, rampant abuse of power, extortion of homosexuals, and perhaps worst of all McCarthyism (heh). Not the sort of namby-pamby McCarthyism that McCarthy practiced, either: The kind of McCarthyism that was both trumped up and resulted in fatalities.
But while audiences liked it twice as much as critics, they still didn't like it that much, and that's a more interesting question. With just over 50% on RT, The Boy was disinclined to see it, but my curiosity was piqued.
The story is roughly based on that of Citizen X, the child serial killer that could not possibly exist in the Worker's Paradise (and so ran amok for years, racking up dozens of kills). Tom Hardy plays Leo, a cop, though the police here are just an extension of the Party apparatus, and they do a lot more exterminating "traitors" than they do solving crime.
When his godson is murdered, it falls to him to tell the child's family that he was hit by a train. (Because, as noted, murder is impossible.) While this is going on, he's given the task of investigating his wife, Raisa (Noomi Rapace, looking exotic, as usual), and her potential treason. When it's made clear that his choice is to throw her to the wolves or suffer serious consequences—well, of course he doesn't throw her to the wolves, and they end up shipped off to Volsk.
Now, one of the really good parts of this movie is the relationship between Leo and Raisa. It is not at all what it seems, but it's the logical consequence of life in a police state, even if poor dumb Leo doesn't understand those consequences at first.
Leo himself is an interesting character. He goes from being a starving Ukrainian orphan to tool-of-the-state with just a brief step in-between for "war hero".
In Volsk, the more traditional mystery aspects of the story heat up, as it turns out children have been murdered in Volsk, too—in fact, all up and down the rail line. Leo's new boss, General Mikhail (Gary Oldman), is paranoid and uninterested at first, but ultimately is won over. Soon they're all taking risks to try to solve the mystery even as the State appears at every corner to crush them.
There's a lot of unpleasantness along the way, and I can see that turning people off. And it's not flawless: There are a lot of threads here, and it takes a good 30 minutes or so for Swedish (!) director Daniel Espinosa (Safe House) to pull those threads taut.
The only other person I know who saw it liked it but was less than thrilled. He didn't care for Tom Hardy's performance which he described as "being Marlon Brando for 2 hours". Also, some of the actors spoke with Russian accents, and some with British, which bugged him. (I don't even notice that sort of thing, really.)
I thought the action scenes were hit-and-miss, but they usually are. And I thought the ending was too neat to be plausible—but this is the first book in a series, and if the ending had been realistic (everyone gets a bullet to the head!) that would both be really depressing and rule out sequels.
So, we liked, but not for everyone. Certainly not for anyone who wants to maintain the illusion that life in the USSR was on a par with life in the US.
Bonus points for self-waterboarding.