Game is not hard at all. The only hard thing is final boss. Other than that it's the same as Crysis 2. use cloak, mark enemyes than start killing them one by one.
2. mark enemies
3. go behind cover and pick one enemy you would like to kill
4. go cloak and aim at the enemy
5. un-cloak and go into armor mode and start shooting enemy
6. when you kill him go prone or crouch behind cover
7. go cloak and move to next cover (enemies will belive you are at the first cover)
That's it. Also, for far away shots don't use burst but switch to single bullet fire (i belive left the button switch beetwen that).
Final boss is pain in the ass. Luckaly there are two 3 check points. For the firs part i went to his left side where there arer unlimited rocket launchers and fire about 10 shost at him. He may pick you up but that will do little to no damage to you.