I liked very much the first 20 minutes of "Case 39" and if the rest of the movie could be as good, I would rate it five stars without hesitations. But in my purely personal opinion, the scenarist greatly blundered by revealing the main secret before even we wathed one third of the film - and the rest of the plot is simply quite predictable and frequently borrowed from other horror movies. Towards the end I simply grew bored.
That being said, "Case 39" is not devoided of qualities. Although not a big fan of Renee Zellweger, I must admit that I loved her performance in this one (the only time before when she impressed me was in the "Cold mountain") and even when the plot started to bore me, it was still a pleasure to watch her acting - especially in a role which is definitely not of her usual kind... also, I really would like that all the social workers have her devotion and courage.
But the real star of "Case 39" is of course Jodelle Ferland who plays Lily, the endangered child. I was already charmed by her performance as Bree Tanner in "Eclipse", but in this movie she showed an IMPRESSIVE talent! She is definitely somebody to watch with great attention, because we may very well have the next Natalie Portman here. And also it is almost impossible to believe, that this cute little girl is in fact 17...
Interaction between Renee Zellweger and Jodelle Ferland is a great show - they both gave the maximum and the result is very entertaining.
So to conclude, I think it is possible to watch "Case 39" and enjoy it, at the only condition that you are prepared that there will be a display of excellent acting by two very talented women, but with a storyline of which, after the first 20 minutes, you will be able to anticipate all the developments, because we all have seen them on the screen dozens of time before.