It's a good film, but I wouldn't call it brilliant myself - mainly because I feel that The Devil's Backbone tells a similar tale so much better. The Orphanage relies too much on its twist IMO, which is a shame, because twists, unless done brilliantly, have become rather hackneyed in certain kinds of movies.
Then again, I have to say that seeing the film at Qatar airport at 4am after not getting much sleep for three weeks? Not the best of times to watch anything.