Great Weapon Fighter is a warrior, melee dps class with decent damage, some defensive skills and decent CC. He may be used as offtank, controller or as high dps class.
Main Ability Scores of GWF are Strength, Constitution, Dexterity. His tactic skill is Sprint, allowing him to run much faster while holding "Shift" key.
This class have fairly simple mechanic: Unstoppable. After collecting enough determination by damaging foes you can use Unstoppable which will set you free from all movement imairing effects and will make you immune to them for the duration of this skill, you will also deal slightly less damage with greater speed and you will take 50-75% less damage (depending on how much determination you had when using this mechanic).
Best races for GWF are Halfling, Dwarf and Half-orc due to matched AS.
Effect of Ability Score on stat per point over 10:
Combat Advantage damage
Damage Over Time (DoT) resistance
Area of Effect damage resistance
Companion stat bonus