Surrounds you with a nearly impenetrable bubble of force; the eight spaces surrounding you are filled with an object called "forcefield", with a appearence and description is identacle to the forcefield outside Grit Gate. This field moves with you, blocking enemy movement and attacks, while allowing most of your attacks through.
Duration: 12 rounds (+3 per level)
Cooldown: 100 rounds.
Aside from a small number of weaknesses and limitations, the bubble provides near-complete protection while active; most enemy projectiles cannot hit you, and most enemies cannot approach close enough to attack you at close range. This makes it an extremely valuable mutation for fragile psychics.
On top of this, most of your own weapons and powers (excluding lasers) can be fired out of the bubble, allowing you to attack enemies with near impunity.
One undocumented feature of force bubble is that it pushes enemies and NPCs; if you walk towards an enemy with Force Bubble in effect, they'll be pushed back provided there is room. If there's no room, however, they'll be forced into the field and will be able to attack you.
Walking an active bubble into wooden fences destroys them.
Finally, note that when your Force Bubble appears, any enemies adjacent to you will be pushed back one space, provided there's room for this to happen. If there's no room, they'll be inside the field and will be able to attack you until you move away.
The bubble prevents you from stepping adjacent to others yourself while active (since it pushes them), making it incompatible with melee attacks.
The shield moves to follow you, but it blocks your view of the adjacent squares, which could cause you to step in acid.
While the description says that you can fire missiles out of the bubble, this refers to physical missiles, like arrows and slugs. The lasers you can create with light manipulation can be blocked by your own forcefields.
While the duration raises with level, at +3 rounds per level and a static 100-round cooldown it is nearly impossible to get Force Bubble to the point where you can keep it up indefinitely without combining it with Mass Mind; therefore, you will want to either gain that mutation or combine it with other forms of defense or escape, such as Teleportation or Force Wall.
Given the high cost of this skill, it may be worth considering the less expensive Force Wall instead, which does not follow you but which offers most of the other benefits, in addition to some increased versitility; it's also easier to get Force Wall to a point where you can keep it active indefinitely.
Finally, there are a few attacks capable of piercing the bubble. Some (but not all) environmental explosions will still hurt you, as will psychic attacks such as Sunder Mind. Very large projectiles can also pierce it, such as the boulders thrown by some enemies in Bethesda Susa.