I think an important aspect of Spec Ops that doesn't get enough attention is the evolving dialogue throughout the game, as well as the evolving aggression.
I'm sure many just breezed right through the game and didn't even really notice the way Walker's execution animations subtly change throughout the game. At first it's somewhat human, snapping their neck swiftly or putting a bullet in their head, but by the end of the game when Walker has completely lost it his execution moves become savage and brutal. Repeatedly smashing the enemy's head into the ground while letting out animalistic sounds. Or even worse jamming the muzzle of the rifle all the way into the enemy soldier's mouse and watching as the muffled soldier frantically screams for help while waving his arms, only to be put down. Fucking brutal.
The soundtrack adds to this as well, with such songs as "Hush" and other popular classic rock songs (evokes Apocalypse Now), but the end of the game has notably more subdued, serene, depressing music that goes a long way in showing you just how far the character have fallen.
I will argue that Nolan North does a better job with Capt. Walker than he does with Nathan Drake. Drake is often one of the most criticized game characters in terms of his happy-go-lucky attitude towards danger and death. Though the game is profanity-laden, it becomes far more angry and depraved at the very end, and especially after the most key moment of the game. I think as much praise that can be put on the game can be put on North's performance as well. Walker goes from telling his squadmates "Kill confirmed" at the beginning of the game to "HE'S FUCKING DEAD" or "Kill is fucking confirmed" and worse at the end of the game is pretty cool to me, I really appreciate that. Towards the end of the game North does a fantastic job in sounding very tired, very weary, and very much like someone who has been through some shit. Overall, I guess I would just say that Spec Ops has better character development than pretty much everything else out there; it's also something I would like to see from more games in the future and I'm fascinated to see more games like this on the next generation of consoles. Could be some pretty wild stuff on there, I can't wait.