But putting money on your prediction is the very definition of gambling, and that seems like a pretty ridiculous course of action when the only thing you have to gain is the ability to play the game a few days/weeks ahead of time.
Or the ability to save $15-20 dollars, which usually takes at least a month to happen otherwise. Unless you pirate every game beforehand, every purchase is a gamble. There's no guarantee that you will enjoy any given game, no matter how sparkling its reviews and word of mouth may be. You are the only one who can determine what you find enjoyable.