A flawless game (IMHO) would literally have to provide potentially endless entertainment to everyone who ever plays it.
People being, well, people this could never happen. Someone will always find something they don't like, could improve, could change about any game. Some people just don't like certain genres or styles of game.
With so many differing opinions on just what constitutes a flaw there couldn't have been a perfect game that could be considered flawless by everyone who plays it - nor should there ever be. We must consistently identify and look for flaws in games so that the next generation of game can be improved and so on, and so forth for ever. A sad day indeed it will be when someone does invent the perfect game - because then there truly will be nothing new to discover and the entire industry would collapse. Why ever buy and play another game then you've experienced the 'perfect' one?
ANYWAY - long, badly written rant aside I don't think there has (or will ever be) a 'perfect' game, but for me - the perfect game would possibly be an RPG that would be able to balance itself based on my play style and react to my decisions as a level-headed human GM would.