I want to say that this is one of those movies that is best viewed without watching the trailers. Trust me they give too much away. This movie is more about story than gore (though there is blood)
Let The Right One In (official trailer) is a Swedish film so it's either dubbed or subtitled depending on your choice. It was remade last year as Let Me In (trailer) here in the states. Both versions are worth watching and although the US remake follows the original very closely the original is still the one to watch.
Why? Simply put because the filmography is beautiful and most of the time bright. The US version is more dark and gritty and to be totally honest I wasn't as sympathetic with Oscar in the remake as I was with him in the original.
If you watch the movie and like it I would also suggest the book. It covers much more ground than either of the movies.