Yep, another FFVII reference. Limit Breaks are separated into three levels of power, with each subsequent level increasing the potency of the ability, as well as the restrictions for its use. For the most part, these are available only in instanced dungeons, and they're a communal resource that the whole party shares. As soon as one person in the group uses it, the meter resets. Most of the actual Limit Breaks are lifted from FFVII as well, and change depending on the class that activates it. As a melee DPS class, for example, you'll have access to Cloud's Braver (using a Buster Sword that materializes out of thin air, of course) or Tifa's Final Heaven, while healers can call upon Aerith's Healing Wind.