I do not want to turn this into another yawnfest NP vs MD thread. the uneven distribution of psychiatrists means that there is a need for other providers to supply mental health care and this includes nurse practitioners. I find it hard to object to the existence of NPs given this (although they too are unevenly distributed and not meeting the needs of the population). I do work with psych NPs and am involved in training psych NP students. All the students are at would be regarded as one of the top schools and yet they all feel that their training does not equip them for clinical practice (with which I agree) and they wish there were more residencies for NPs (there are some additional training opportunities at the VA in particular). I don't think that NPs are good at managing risk and seem prone to admit everyone when a psychiatrist would be able to manage more challenging patients in an outpatient setting. They do not have a good grasp of descriptive psychopathology, or the ability to come up with nuanced formulations of patients. They are not good at managing patients with complex comorbidities. They are not good at managing high risk suicidal, self-injurious, violent, or homicidal patients. They are not comfortable usually dealing with pregnant patients. They are not adept often at using older treatments such as TCAs (not baby doses, real antidepressant doses), MAOIs, and often use curious polypharmacy. Many of the criticisms that could be lambasted against NPs also apply to bad psychiatrists (of which there are many). I think that NPs can work very well with good supervision from a senior psychiatrist but this is rare, and psych NPs are increasingly working completely independently or with superivision which constitutes little more than signing the charts.
Most of psychiatry really isn't rocket science but the field is prone to fads, dumbing down, pseudoscience, and mental masturbation and a high tolerance for poor performance from its practitioners. I do think it might be reasonable to train seasoned mental health nurses to do a half-decent job in dealing with 80% of general psychiatry in 2 years but this doesn't seem to be happening.