The Adept is a versatile spellcaster with access to many of the best spells available. However, the Adept pays for this versatility by improving in caster level more slowly than other spell casters. This means that Adept spells are less powerful, and it takes Adepts longer to gain access to higher level spells.
Adepts have skill with a good range of weapons and can generally be effective attacking in combat. However, they can usually only afford to wear light armor due to their relatively high spell failure and have limited hit points, so Adepts can be somewhat fragile on the battlefield.
Charisma is the most important ability score for an Adept, as it controls all aspects of an Adept's spellcasting. Dexterity is also very important for increasing the Adept's survivability and for affecting ranged combat strength.