To chime in here, albeit a week late, it's not just media hype. There really is a large peer-reviewed literature supporting ketamine's rapid antidepressant effects in both unipolar and bipolar depression, most of which studying the effects of a single IV infusion. Whilst highly effective almost immediately, the problem is that the response is not sustained and tapers off after a few days. Other studies have demonstrated that repeated infusions can prolong this effect, and is well tolerated, although very few studies have focused specifically on longer-term negative side-effects, or on the actual long-term outcomes on affective disorders themselves. (Personally, I would say that the potential harms of a single dose are significantly less than those of an under-treated depression!)
You are right when you say that we should exercise caution, and this area definitely needs further study. Very often, though, patients with treatment-resistant conditions are desperate, and should be provided a safe space in which to try novel treatments, and I would also agree with your *edit* in that post.