Sorry, I'm getting tired so this response won't be as complete as I would like. Disclaimer: all of this is based on my own experience and I don't know how much others differ.
Ketamine was great. I've been around the mental health world quite a bit in the past few years and tried all sorts of treatments, and one of the things that surprised me when I started ketamine was how much they let you flounder with less effective stuff before doing ketamine. I remember reading the wiki article on it and the success rate was incredibly high compared to other things I'd tried before.
In case you're going in expecting to have a mild experience like with most medications, don't. The first session at the reduced dose I mentally was in another dimension. It's not uncomfortable or scary, it's just also not subtle by any definition. It wears off quickly, for me almost always within 45 minutes if I slept the night before, and those 45 minutes never felt way longer. My tolerance built up quickly and twice a week for the first month ended up with less impactful sessions than when I went down to once a week. If I skipped a week or two the next session was pretty much back at full strength.
The goal is to wake up some of your neural pathways you've neglected to use while depressed. Think of it as hiking trails through a forest that have become overgrown so you stick to the comfortable, well-travelled ones (depression). What this means for what you might experience is the awakening of some of your demons so you can confront them and leave them behind. The good thing is that they're not scary in the moment, but you likely will come out of some more intense sessions feeling some ways about stuff. After the whole thing I would say definitely worth it, and I'm the "avoid anything even slightly unpleasant at all costs" type. ETA: I also had a lot of "epiphanies" about stuff I already knew that helped me see reality in a different way. For example, I already knew that most of my issues were situational, but through these sessions I realized that if a problem is from something outside of myself, that means it's not evidence that there's something wrong with me. I know it sounds silly when written out, but those are the types of revalations I had and that specific one has been one of the strongest tools I've had since then.
Ketamine was the last treatment I did for my depression, a rather severe case with one of the episodes lasting a few years and a serious suicide attempt. Depression is no longer on the list of things I feel the need to actively work on (apart from small maintenance to my thoughts) and I've discontinued all of my depression meds that I was relying on before that.