Buying a Game

I have 3 different ways to decide what game I'll buy (To my Playstation 3).
First of there is the obvious "fan" waiting for a game to come out since the very first news. Like buying the game on the very first day. With this method I bought Mirrors Edge, GTA4 and will absolutly buy Final Fantasy 13.
Then there is the impulsive style. This happens when I have alot of extra money and are somewhere in the middle of waiting for the next game to buy. Then I just go for the current best game out or something strange/special game. With this method i bought Battlefield: Bad Company and Saints Row 2, but also all the Playstation Network games such as Savage Moon and Flower.
The third method is similar to the second but requires alot of extra research. Right now i'm in that dilemma. I have some spare money and I feel alittle bit bored so I either buy a game or wait. Thought now i'm leaning towards buying a game and i'm not sure which. Going by the second method it's currently Killzone 2 that is in a good position but i'm not sure. Buy it or wait for something else. I'm not good at these decisions... :(