If you like our movies and gore, try Claire Denis' Trouble Every Day. You won't regret it.

"I think working around a bunch of nurses is giving you a false sense of your ability to intimidate."

I agree though I find most foreign horror films to be far superior to US ones. Besides Martyrs and Inside, another French horror film I enjoyed was Frontiers. I liked it better than High Tension.

Yes, the French make great shock horror films. There's also "Irreversible" and "Inside My Skin". Don't know if you have seen them, but there are also two French-Danish films, "The Strange Color of Your Body's Tears" and "Amer", both excellent.
Love "Martyrs", can't believe they allowed a remake to be produced. I haven't seen the remake, by choice, looks like garbage. That's a film that shouldn't be remade, the original is perfect. Haven't seen "High Tension" but I'm thinking about giving it a go now.
One last suggestion since you enjoy horror and terror films, if you haven't seen it, it's not French, it's Dutch, but man, what a superb little film, "Borgman".