As for the main argument, I think Spec Ops mostly succeeds at what it attempts - which, to me, is to show the excesses of war and adolescent power-fantasies. I've pointed out before that the story is somewhat clumsy and forced, and that it's a bit depressing that even despite that it has generated so much attention - it just goes to show how starved we are when it comes to gaming narratives.
That being said, I don't really agree with the argument that if *I* had made choices instead of Walker the game would have made a more lasting impact. I think it succeeds at what it tries to be - you see Walker's story, and you reflect on that based on your previous experiences with other games and war-related media. You don't need to feel you are Raskolnikov to enjoy/reflect on Crime and Punishment, and I think the same applies here. I think your argument relies on the premise that games can offer "deeper" immersion than books/movies/etc., but that is highly questionable (I would say games can offer a different kind of immersion, but it will always be limited, just like with books/movies/etc.).
And yes, do play it on easy - if only to make the adolescent power-fantasy even more absurd, which enhances the game.