Here at VGrevolution we use a very simple ratings system when reviewing games.
We base scores off of a point system from 0 to 10. 0 being a game is pure garbage and 10 being the game is the best game created.
When reviewing, we look at many different aspects of the games which vary from genre to genre. We rate 5 categories and then create an average score from those 5 ratings:
Includes game modes, controls, and Online Play
Includes any story presentation, menus, and HUDs
Includes how the game looks and use of effects
Includes how the game sounds and its overall soundtrack
Determines whether you are going to play this game often or not
Takes above categories and create a 10 point average score