Some casual gaming is possible, by turning down your resolution to 1440x900.
CASUAL gaming??? Are you kidding me?
Apple basically packed in for a first time a GTX mobile card (the 650M GT of the rMBP is clocked higher and faster than a standard 660M GTX), that beats 'gaming laptops' such as alienware m14x which are double the size and weight, in a air-like chassis thick 0.7 inches and weighting less than 4.5 lbs.
This machine is able to game ANYTHING, even hardcore gaming (BF3, etc..) at 1680/1920 ultra settings 60+ fps, and can even go native res 2880 high/ultra settings on very recent games (civ5, skyrim, diablo 3, etc...) with decent 30+ fps.
The only way to go higher than that on a laptop is with 17/18'' monster laptops with single/dual 680M GTX cards or similar where the card alone consumes more than the whole rMBP.
Pretending more in that size and weight is like pretending to have a 800 hp car which does 20 km with a liter of gasoline.
It's quite simply not possible.