The Hills Have Eyes question?

I normally like psychological horror like 1408, Rosemary's Baby, The Omen, Disturbia. I am usually left cold by movie like House of Wax, My Bloody Valentine, The Texas Chainsaw Macre. I thought it would be safe to see but it really got to me. Why did this gory horrorfest get to me like no other ones have? I am guessing that it set me up to actually care about the characters? I suffer from panic attacks and didn't want to go anywhere for hours after this one.