What makes you decide to buy a new game? I can think of several factors that lead me to buying new games. I can't say just one thing usually makes me decide.
I am big into word of mouth. If most of my friends in my guild start discussing a game on vent I am usually all over it. I don't even have to see the game to have the urge to buy it.
The price is sometimes a factor. If I want a new release I have no problems paying the $50+ for a preorder. After Christmas Steam had some $5 games that I always wanted to try, but was never willing to pay full price for. I bought EQ2, Eve, and SWG's. I figured I blow $5 on energy drinks every day so why not? I would have at least something to show for my money by buying the games. I may end up finding a game I really like.
Watching video game trailers is also very addicting, and I fall for games so quick. I know after watching the Call of Duty Modern Warfare 2 trailer I wanted to stand in line at midnight to buy the game. The graphics and gameplay looked really that good.
In MMORPG's I love to preorder collectors editions for the usual head start, and freebies. I only like to play MMO's from the ground up. I like to get that jump, and not be a noob joining an MMO a year after release.
Burnout also plays a huge factor in my game buying decisions. A new game usually gives me the excuse to leave the game, and buy the new one.
What makes you go out, and buy a new game?