A pen knife is ideal for removing the plastic wrap, but a box cutter also works just fine. I remove the plastic wrap completely, but if you want to keep it in place, you need to be very precise with your cut along the top flap to avoid box damage. One recommendation would be to use something very small, such as a pin, to punch several sequential holes in the plastic between the top flap and the front of the box. This gives you a place to insert a one-sided blade with the sharp edge angled up to complete the cut.
The key to opening the top flap is to approach from the sides. Slide a thin, sturdy object (such as a thin letter opener or the blade of a knife) under the top flap from one of the sides, then lift straight up. DO NOT ROTATE, JUST LIFT. If the flap doesn't lift easily, do the same thing on the other side to make the elevation symmetric and prevent a bend. Your fingers should be able to do the rest.
I've opened dozens of new games and never damaged a box flap with this method.