I rather think this was as good as Hollywood could do with this one, particularly if aiming for this certificate (though Transformers made a 12, and with that language, I remain amazed, though it's otherwise suitable only for the under sixes). I always felt the book to be a rather adult book with kids in it, and this definitely moves more towards the kids than does the book.
However, it is a very entertaining movie. Most of the key themes from the book, including the final battle and aftermath are there, if toned down. The bullying and outsider themes that made such an impact on many of us are still there, and the effects all you could want. The battle room in particular is well-realised, though some sequences I'd have liked to see were missing.
Pretty much all of the cast and characterisation are fit for purpose, Ford and Kingsley reliable as ever, Asa Butterfield fine again, but I felt the sergeant was feeble- straight out of "The Sarah Jane Adventures" or that lost non-classic "Five Go To Boot Camp."
Still, overall, an enjoyable, perhaps languid, but never too slow, passable adaptation of a fine novel; one that will deserve another watch.
A job well done.