The Personal Energy Shield provides protection from most weapons and attack methods. It does not protect you from the Dioxis Grenade, Scatter Gun, Cycler Rifle, Disruptor Rifle, Lightsabers, Princess Leia's Trooper Bain ability, Boba Fett's Flame Thrower, Emperor Palpatine's Force Lightning, and melee attacks.
Though it protects you from blaster fire, it also doesn't allow you to shoot out. Weapons like the Cycler Rifle also count. Pressing the activation button while the Personal Shield is active will turn it off, and force you to wait until the card can be used again.