This movie got uniformly rave reviews from both critics (96% on the Tomatometer) and movie buffs (#41 on IMDB's top 250 films of all time). It won three Oscars, and was nominated for three others.
The premise is stunningly original. A little girl, Ofelia, is taken with her remarried pregnant mother to live with her new stepfather. Their new home happens to be a portal to a supernatural fairyland, which Ofelia proceeds to explore.
That doesn't sound so bad! But—oops!—it's set in 1944 Fascist Spain. The stepfather is a cruel and sadistic brute, a captain working to put down the resistance, and Ofelia's new home is also an army outpost. Both the natural and supernatural worlds are filled with dangerous monsters, ready to pounce at the slightest mistep, and outbreaks of sudden explicit violence and death.
So there you go: it's very dark, and not for the kiddies! Might not be for you, either, if you prefer movies where all the good guys wind up OK at the end.