The film is a 15 in the UK.
Knocking my world askew, The Torygraph likes Serenity (NB. the linked to page has gratuitous breasts from some other film and so is probably Not Safe For Work...):
A complex ensemble piece without major stars, it has characters to care about, a keenly political intelligence, and some of the most cracking banter since Howard Hawks was in his prime. It deserves to be a huge hit when it's released next month.