A gaming mouse will give you that little bit of an edge when it is needed the most. There are various things to consider such as what type of genre you play the most, perhaps you need a MMO (Massive Multiplayer Online) mouse or rather a FPS (First Person Shooter) Gaming mouse.
Higher DPI makes for better response and of course the light system is also important. The biggest part of your decision should be made on comfort though. You will be holding and moving your mouse as if your life depended on it most of the time, and you do not want that to be an uncomfortable experience. Comfort and weight goes hand in hand, some mouse can be weight-adjusted, others you need to make sure that the mouse has the right weight for your playstyle.
You will find that Computer mania has a massive range only the best in class brands of gaming mouse, which will make finding the right one for your hands much easier.