This is a very strong spell for mystics in multiplayer games and the more people you are playing with, the stronger it becomes. It is similar to Dynamite Blast except that it only deals 2 damage and requires you to succeed at a Fight test, though you can choose the weakest enemy at your location to fight. Those drawbacks are balanced out by the fact that it costs 2 less resources and is in a class that is substantially more likely to have spare resources to play it. Additionally, it synergizes with other popular mystic cards such as Arcane Initiate and Uncage the Soul. Finally, and possibly most importantly, it is much easier to arrange multiple enemies at a location that contains investigators than an empty one where Dynamite won't hurt your fellow players.
Storm of Spirits is especially good in Sefina Rousseau decks, where it is possible to play Storm of Spirits two, or even three times in a single turn, clearing a location of even tough enemies. And for the truly bold, it can be combined with Double or Nothing though I haven't personally tried this combo yet.