A perfectly serviceable little thriller that I probably won't remember in a few months but which I didn't walk out of angry at - hey, you take what you can get with these kinds of things. The Boy easily could have been a ninety-minute heap of insulting garbage, and it's not! Bully for us! I find Lauren Cohan to be extremely likable; she's one of maybe five people I can still stand on The Walking Dead, and tasked with a load of silliness here she proved that factor's not a fluke. She sells what she needs to sell and you're concerned for her the right amount when the bad stuff starts happening.
As for the ending (there be spoilers after the jump)...
... early on I'd guessed a couple of outcomes, and one of them was indeed that Brahms, the dead little boy that the doll was a stand-in for, hadn't actually died and was living there in the house behind the walls, moving things around and making it seem as if the doll was doing it, and sure enough. (The movie tried to make us think that the character played by hottie Rupert Evans might be grown-up Brahms, but I never bought that.)
What I didn't expect though was for the Brahms to be a hairy sex beast when he emerged! On IMDb they do a good job of covering up who this dude's playing but the actor is named James Russell and, as if the counter-act the whole "boy" thing of the title, the film positively luxuriates in his chest hair and beard, and it was like a hurricane of pheromones blustering off of the screen. Granted his face is covered with that eerie doll mask, but it still worked. It was a look. I was down. I'll tuck you in, Brahmsy.