Having no ability to stomach any type of gore in movies, I opted to read the book instead. As always, it's much more in-depth – and several elements that are in the book have been left out of the film, such as the paedophilic nature of Eli's ‘guardian’.
The book is certainly gruesome, and very disturbing in places but I found myself totally drawn into it – Lindqvist manages to make you pity/feel for Oskar in a way which allows you to look past the things he does, the things Eli does for him – and genuinely love the two characters and cheer them on. Definitely worth a read, especially if you're wanting more depth than a movie can offer.