If you're easily offended, or don't like comics/violence/juvenile humour this film isn't for you.
If you like well written, well acted, all out comic style fun with a bit of a twist you'll love it. Don't let the bright colours and comic background styling of the cover fool you (as some seem to have done!), this film is definitely for adults or older teens only. The violence starts off fairly realistic, but quickly goes to comic-y/Kill Bill style when our child protagonist appears. And what an appearance! I haven't fallen for a character so quickly in a long time, and rarely a child. Hit Girl is a joy to watch because of the joy she seems to take in her 'work', (which, by all accounts, Chloe Moretz did) and the score complements the action perfectly to enhance this perception.
I laughed out loud more times than I could count, and winced and groaned a lot too. As well as a lot of violence and 'language' this film has a lot of heart, with characters you can care about - even Red Mist is a fairly sympathetic character for a lot of the film.
This is one of only 3 films I've seen more than once at the cinema and I could have gone another 2/3 times if I had the money/time.