Charisma - Affects Group Tactics, Social Skills, and the Telepathy Mutation Path. Many missions can only be undertaken by characters with a high Charisma.
Coordination - Affects the Athletics, Armor Use, Dodge, and Melee Skills, as well as Reflex Save. Raise your Coordination to increase your Defensive Abilities.
Dexterity - Affects Pistol and Rifle Skills, along with Reflezes Save. Dexterity increases long-range Offensive Abilities.
Endurance - Affects Health, Stamina, and the Body Save. It factors into Armor Use, Athletics Skill, and the Empathic and Patho-Transmission Mutation Paths. Endurance increases your survivability.
Intelligence - Affects Gamma, First Aid, and Group Tactics Skills, all Tradeskills, Nano-Manipulation, and Telekinesis Mutation Paths, as well as Mind Save. Raise Intelligence to max out the First Aid Skill or to use Mutation Paths and Tradeskills.
Perception - A secondary component in many Skills, including Dodge, First Aid, and Pistol. It factors into Sonic Influence, Suppression, and Thermal Control Mutation Paths.
Strength - Determines Body Save, Encumbrance, Melee Skills, Primal Mutation Path, and Health. Raise Strength if you wish to play a melee character.
Willpower - Primarily determines Stamina and Gamme Attributes, as well as Mind Save. All Mutation Paths factor in Willpower, so raise it if you wish to use Mutations.