It's weird how a lot of people just don't get it
The very intention of the series is to be a true serial killer movie in the sense that it's not some guy with a mask killing naked teens in one location. It's trying to come as close as possible to creating the look of home video footage of a serial killer. There are lots of corpses, torture, and unspeakable cruelty but there's also lots of footage of them just hanging out and talking. The point is that they are still human and they do like to do normal things, they don't run around stabbing people 24/7.
When I first saw all 3 movies, I hated it but after reading interviews with Fred Vogel on just what these movies were made to be and watching it over with an open mind, I really appreciated what he was going for. It's not watered down crap like Hostel or Saw, this is raw, gritty, and the violence is not made for entertainment, it's just a really disgusting and brutal portrayal of violence. You're not gonna say "OMG his head just flew 20 feet in the air!" you're going to feel uncomfortable because it's the intention. These are murders and what gets them off is what fascinates us but seeing it firsthand really makes it harder, I mean imagine seeing the crimes of Dahmer through his eyes... that wouldn't be fun.