3D sends a different image to the left eye to the right, and the glasses for these screens flicker appropriately to only show one image to each eye.
From what I can gather, If the sync for the left eye is employed in both lenses, the screen will display Gamer 1's screen. If the sync for the Right eye is used, then similarly the right eye will show Gamer 2's image.
If you have the usual sync on the glasses, you will see both images - one in each lens.
If it is a sufficient advantage, you could play with your game screen, one eye shut, and peek at your opponent's screen by switching which eye you have open.