Killer 7 is a unique and visually appealing piece that is not meant to be entertaining for the average gamer.
Simply put, the mechanics are very linear.
There is a upgrading system, which gives incentive to actually think out each enemy type you face, then the simple button mashing technique. By doing so, you can improve your aim, power, reload times, amount of ammo, etc.
The main selling point for this game, is the visual aesthetic. Not many games have used cell shading graphics, but Killer 7 does with such finesse in style, that it really is impressive. Plus the cinemas throughout the story are in anime form too, but not in the traditional sense of it. To add on to that, the story is one of the most bizarre ones yet...making how to decipher fact from fiction hard, with the constant dream state reality the game seems to be constantly in. Though I guarantee that it will come together as to why at the climax.
To synthesize how good killer 7 is, it is only average. The game play is decent enough and does have depth to keep the player's interest, but does become mundane at times to NOT be completely entertaining to today's blockbusters. Making it the only reason i would not recommend it.
Though if you want a very original and eccentric experience, without minding the tons of violent and somewhat disturbing scenes you will encounter at times, you will sure be enjoyed with the superb eye candy :)
-Mj