I’ve enjoyed a few French BD’s and up until I read this thread I thought they called them whatever the French translation of Graphic Novel would be.
If you like eldritch inhuman horrors, you might like Hakaijuu. I haven’t read it, but I’ve seen some of the illustrations. And of course there is the aforementioned Junji Ito.
It’s not that it deals with eldritch horrors – it’s relatively easy to come up with disturbing concepts or images. Parasyte takes the “Body Snatcher” concept and runs with it in various directions, exploring the implications. (What if you found yourself bound to an imperfect body snatching, so that you controlled your body but the alien controlled your hand? What if you learned that an alien inhabiting a woman’s body wanted to get its hands on a human baby – and finally did?) it imagines a culture and personalities for the aliens, as well as the humans. But you can’t just “get along” with the aliens if they insist on eating unconverted humans as their steady diet.