I would say it conquers major anxiety and mild to moderate depression. It's excellent for SAD, and used to be advertised as the 'Sunshine' drug.
My SiL is a mental health nurse. She says it works very well on most people, but can have adverse effects on a few. I asked what she thought was the worst effect that she had seen, and she said some people could be a bit more spaced out than usual, but felt that they were the sort of people who would have problems finding anything suitable for them. Like DBH. He always complains of a fuzzy mind when he takes anti-depressants.