Might I suggest we seperate high-realism (such as Call of Duty, because it's got a realistic setting for the most part) and high-authenticity (like ArmA and Red Orchestra, for their attempt at simulating combat)?
What a lot of people seem to think is that this thread is about what I call realism, when it's about "authentic" shooters, which I'll hazard to say CoD, BF and Spec Ops don't qualify. When I think "authentic", I imagine ArmA or Red Orchestra series, among others.
I think for a lot of people just have the wrong idea when they think about "authentic" shooters. They think it's about walking a mile and then getting shot by someone you didn't see. Even if you actually try, say, Red Orchestra, odds are getting picked off every time you run a bit too far might make it seem like you're supposed to be hiding all the time, so you give up thinking it's boring.
Obviously there are just people for whom it's not their thing, seeing as fun isn't a quantifiable value. I can enjoy watching hockey and curling but not soccer, so it's only fair to say it works that way in other domains for other people.
But when someone says "Just join the army if you want realism," well, dudebros gonna dudebro.
Although in my experience, once you learn the dos and don'ts, having high authenticity is way more intense than, say, Halo. Just the feeling that out of all your squad-mates who were moving in with you and two of your buddies avoided enemy fire and are now clearing a building room-by-room with your bayonet and a handful of grenades. Or furiously spraying your .30 cal while the Japanese team makes its final desperate banzai before the time runs out, only to notice your gun is starting to smoke and wonder if you have time to change your barrel. Nothing makes me harder.