Although this spell is cheap and has good duration, it has a downside if the tactics are enabled: party members will still select affected enemies as combat targets and will need to be micro-managed.
Though moderately useful as a shutdown skill, the true value of Force Field lies in deploying the spell as a defensive mechanism, in particular in synergy with talents that already immobilize the user (such as Captivating Song or Stone Aura). Additionally, casting Force Field on a party member that can generate a lot of base threat (e. g., on a tank after Taunt) creates a perfect tank that takes no damage.
When used on the offensive, note that the spell grants merely damage protection; non-damaging spells and abilities that apply penalties will still work (Affliction / Vulnerability Hex, Mark of Death, Cone of Cold's movement reduction, etc.). The spell thus can be used to incapacitate enemies while debuffing them and making them more susceptible to damage.
The spell is very useful in combination with Walking Bomb, as it will protect the caster from any damage while the target slowly dies of poison.
The spell does not make you immune to either Dispel Magic, nor the Force Field itself. This can be a blessing as well as a curse, depending on the situation. A second Force Field cast by another team member will double the duration. Dispel Magic or Anti-Magic Burst cast by another team member will allow you to free yourself from the paralyzing sphere prematurely, if needed. Beware, however, lest enemies cast Dispel Magic on you, since this will disrupt the sphere.
A party member who is the victim of Crushing Prison can have Force Field cast on him/her to dispel the Prison. Since this creates the Shockwave spell combination, it's recommended you don't do this when many party members are nearby.
Casting Force Field on an airborne target will lock them in the air for the duration of the spell.
Useful as an emergency tool to save a party member from "certain death" attacks, i.e. tossed around like a doll by a dragon. Cast this spell on the affected party member as soon as you notice they are in peril. The attack will cancel and the attacker will move on to a different target.