The Mage is the spellcasting role that is most in tune with the true nature of magic. Mages gain access to new spells more quickly than other spell casting roles, and have by far the best offensive spell selection.
The Mage's biggest weakness is melee combat. With very few hit points and usually without any armor, Mages can fall very quickly on the battlefield. They also suffer from having only the most basic weapon training.
Intelligence is the most important ability score for all Mages, as it controls all aspects of their spellcasting. Constitution is also very important for supplementing the Mage's very limited pool of hit points.