How sophisticated and violent can YA books be?

I read a book recently that I really enjoyed, and I'm a 24 year old woman. It was supposed to be a horror story about Christmas (Yearly Harvest), and it was marketed to the Young Adult audience, so I wasn't expecting much. To my surprise, it was surprisingly sophisticated. Very deep characters, and compelling solid drama, all with the backdrop of a creepy - yet realistic - town. And it's not GORY, but there is a scene where a mutilated body is shown, and one or two other parts where something nasty happens out of the character's sight, but they hear it. My question is - is that really Young Adult material? I mean no offense to anyone here, I typically don't read YA but this caught my attention and I was curious if it's the norm for such books. If so, I may read them a bit more. Especially this Twilight everyone is babbling about, lol. Thanks.