Yup. I'm not massively squeamish or anything, but combined with the darkness of the themes, it caught me a bit by surprise. There are some fantastic performances (Ellen Page is tremendous), and the fast-paced, low-budget filming feeds into the pace and energy of the film in a positive way. Good soundtrack too.
If you want more of Ellen Page being tremendous, Mouth to Mouth is good: http://www.imdb.com/title/tt0383518/