The Texas Chainsaw Massacre
I will only say this...it is poorly lit and very familiar. Familiar in the sense it is a slasher movie on very small budget.
The truth is, I sorta dug The Texas Chainsaw Massacre. It's not very violent, but it's raw and macabre. I, personally, liked it quite a bit.
I enjoy any film where there's equal opportunity. Being a paraplegic, I just loved watching the guy in the wheelchair get it. :)
haven't seen The Isle, but I don't know why Texas Chainsaw Massacre would be any more disturbing than any other slasher flick.
By the way, don't know if you've seen it, but you may think Croenenberg's 'Crash' disturbing: it's about people who are sexually aroused by violent car crashes.
Also, Man Bites Dog, which is a fake documentary following the exploits of a serial killer (though not necessarily more disturbing than any other serial killer film, I guess).