It's very promising for the so-called "extrapyramidal" disorders. Interestingly, though, there are a few
studies demonstrating a positive correlation between DBS and suicidality in patients with Parkinson disease and other extrapyramidal disorders.
For what it's worth, many patients report that electroconvulsive therapy (ECT), the "electro-shock therapy" once common in mental hospitals and portrayed nightmarishly in film and fiction, is the closest thing to a miracle cure for their otherwise intractable depression. Some patients report that it works pretty much instantly and feels like a fog is lifted.