It's a simple game but still fun. I feel that a big part of why the game is fun to play is because the controls are so responsive and because the sound-effects are quite good..
The beginning of the game was somehow innocent, you're just beating up bats. But in the last stage the game got really brutal: guards shooting you on sight with shotguns (great attention to detail, btw, how the guards are reloading their guns), and then you are beating the guards to death from behind with a blunt pipe. Somehow the sound-effects made this feel very realistic...