"God and pigeons are one. Trust the numerous pigeons."
No matter how popular a game is, there will always be at least one person who doesn't have much fun playing it, but for the most part, many of the best games are those that appeal to everyone. A good deal of this has to do with the fact that compared to other media such as movies, it's easier to determine the aspects that make a game fun. The problem with this situation is that often, you're left with several generic titles that, while they are fun on an individual basis, fail to stand out in a crowded market. That is why the hardcore niche games, including Killer 7, are still around. Yeah, it has it's fair share of problems, and many people will absolutely be disgusted with the gameplay, but even haters will be able to appreciate the various touches that make this game so different.
In terms of narrowing down a genre, the closest fit would probably be a hybrid FPS/adventure game. The controls of this game reflect that unusual nature. A button causes your character to move forward and the B button is used to turn around. In terms of movement, that's pretty much it. To go into a first-person perspective, you hold the R button, which also gives you the ability to use special attacks and lock onto bad guys.
One of the game's major faults is the that you don't have full control over the camera. In order to give the game a more cinematic feel, the camera is fixed during movements, and so if you're not careful, you could run right past an enemy hiding behind you, unable to see him.
The gameplay itself is a little bit on the simplistic side. It feels somewhat reminiscent an obscure game called Maken X for the Dreamcast. Your movement is extremely limited and puzzles aren't very challenging. However, the game still manages to be fun, helped in large part by the visuals and story, but also because of this unconventional gameplay.