We need to talk more about Realistic Mode. There's barely any info about it on the net.
This is what I've gathered so far:
1. You die from two or three shots
2. Enemies also die from two or three shots
3. Moving from cover to cover while the enemy is watching will most likely kill you
4. Enemies spot you much faster
5. Enemies won't walk into your traps as easily
6. The difficulty is unlocked from the start
I can confirm everything but 2 and 5.
2) The normal enemies die from one or two shots. But then their are higher tiered guys with armor that take more shots (not anything obscene, except for the odd "heavy" guy)
5) I haven't really tested this so I can't say one way or the other.