#2 - Your throat is ripped out by big, scary dogs!
Alarming, this. A sneaky mission into the wastes of Chernobyl kicks off with an easy sniping opportunity, to let you feel your way into the softly-softly approach. Mess up, though, and things quickly go pear-shaped - worsened by the horrifying sight of three slavering dogs launching themselves at you through the long grass.
Men with guns, we can handle. But dogs? Christ, these blighters move like greased lightning and are simply impossible to avoid, especially in packs. We want our mummies!
#3 - You spend all your time in enemy territory
Unlike previous Call of Duty games, there's no no-man's-land here. No allied country to liberate. You're fighting (or desperately trying not to fight) in your enemy's back-yard. Where they have tanks, bases, patrols and lots and lots of heavily armed soldiers.
Later on in the Chernobyl sneaking mission, you're trotting across an open field when, Ohmygod!, a full-strength patrol appears on the horizon. You spend the next moments inching slowly forward, as tanks almost rumble over your feet while you attempt to judge each soldier's movements so you're not stepped on.
Try not to whimper.