It depends on what kind of game you play. If you are into FPS (first-person shooting) games like Call of Duty, you will want a gaming mouse that has a good “DPI” and the shape of your mouse should be designed for low friction, so you can quickly turn and aim at your oncoming enemies.
_% of your success in FPS games is going to depend on your mouse. If you are playing MMORPG (massively-multiplayer online role playing games) such as World of Warcraft, then you will want a gaming mouse with 12 or more buttons. It will also be good to get a mouse with side buttons that can be used to change weapons and rotate in the game. You may also want a mouse with a “scroll wheel” for quick movement in game.