Apparently Valve had originally had some gel in their recently released Portal that was much like the gel that made you slide/run faster and the gel that made you jump higher. This gel though let you walk on the sides of walls and although very innovative, Valve decided to take it out of the game because the disorientation quite simply made people sick to their stomach.
Lead Writer Erik Wolpaw stated “At one point we had a new Gel that allowed players to walk up the side of walls. While this added a new twist to the game, the effect was so disorientating that it made people nauseous..” I don’t think I would have had any problems with it personally but after seeing this Valve actually went ahead and change the movement as well as the frame rate to tone down any other areas of the game may have induced nausea.
