The thing that made me stay is unglamorous: it is a folder of markdown files on my disk. Every other notes app I tried before this one, I eventually had to think about how I would get my notes out of it. With Obsidian that question never comes up, because there is nothing to get out of. They are already just files.
That sounds like a small thing until you have been burned once. I have moved machines, changed editors, and started reading my own notes programmatically from scripts, and none of that required Obsidian's permission or an export flow.
The second thing, which I did not expect: it turned out to be the best place to keep context for AI tools. Because it is plain text in a predictable structure, anything can read it. My agent setup reads the same vault I write in by hand. No sync layer, no API, no format negotiation. That was never a feature they advertised to me, it just falls out of the file-based design.
Where it is genuinely weak: search. It finds strings well and ideas badly. If I remember roughly what I thought but not what I typed, I am stuck browsing. And the plugin ecosystem is a real strength that is also a real tax, because a vault held together by nine community plugins is a vault that breaks in nine ways.
Still the tool on my list I would replace last.
Logseq