You know, I'm kinda mixed about the firearms. On the one hand, I know I'm a great marksman, especially in video games (remember boys, aim small miss small) but there were times when I couldn't hit the broad side of the barn. and then immediately after, three headshots in a row! Then I read an article where the devs stated they did it on purpose to add to the chaos of the story and environment. And going in knowing that, it makes sense and it creates this crazy awesome vibe like I'm stuck in a John Woo shootout. I heard the multiplayer mechanics handle differently but I have yet to play it.
Yeah, the multiplayer engine handles firearms in a straight forward kind of way. You point at it, you're going to hit it. Shooting full auto creates lift, headshots put you down, no matter how armored you are.