my impression that "standard" anti-depression drugs are neither particularly effective nor free of serious side-effects. And things which are more effective -- like ketamine -- are very rarely prescribed.

More or less, but it's a question of levels. SSRIs didn't do much for me and a lot of other people, plus weight gain sucks (luckily no sexual dysfunction), but they're not particularly dangerous from what I understand. Stuff like Bupropion is awesome, as long as you don't mind sobriety and have a low risk for seizures. There's other drugs which modify SSRIs too, but I've never had any and they're supposedly more on the 'side-effect-y' side. New stuff like Ketamine is waaay out there, like almost on par with electroconvulsive therapy, in terms of how likely you are to see it but IDK what it's like in terms of safety.

But once the 'trial-and-error' portion of dosing is over with though and you're on something that works for you, it's absolutely night and day. I can only speak for myself obviously but it was a complete perspective switch, like someone flipped a switch in my head to 'not miserable.'

(Obviously I'm not an expert, just a guy who's spent some time on the patient end of things. I am really interested to hear Yvain's answer if he has one.)