The gameplay in Spec Ops: The Line is terrible and repetitive, with an overall tiring effect. And this helps strengthen the experience's narrative significantly.
For me, the gameplay becomes great by being terrible. Because it helps you becoming further immersed into the stressed and disconnected feel of the setting that builds up from the first chapter until the very end. Because war, violence, killing other people, is not fun. And never will be. It's why it is so prefferable when your targets are just dots on a video screen to be wiped off with the press of a button, or just raving lunatics that attack you for no other reason than that they can, without any capability of appearing vunerable or emotional. If you could see the face of the person, or learn anything about who he is when you are about to aim your crosshair at him, it might not be as easy to pull the trigger. But then that is all you really need to do. No other effort is required apart from just pulling a trigger. Pull the trigger and it is over. A lifetime of experience cease to exist in a split second.
The feel of tiring repetition helps simulate Walker's desperate attempts at walling himself off from the fact that he is doing the opposite of what he was meant to do. The killing just becomes a chore, a routine from room to room, from building to building.
Get the job done. Just do it. Do not think about it.
Yet thinking is what the human mind cannot stop doing.