I keep a gaming journal, but it’s only for thoughts afterward. I keep it much simpler than I used to, as there’s a point where writing at length becomes work, and gaming shouldn’t be work. That’s the same reason I don’t keep a backlog. In my longer posts here and elsewhere, it tends to just be stream-of-consciousness writing derived from those journals entries, just cleaned up a little bit.
As for note-taking, I will almost never take notes on opinion/criticism during a play. Pretty sure that again, it’d feel like work if I took notes. I also rarely write about games I don’t finish unless I’ve played most of them (I tend to bounce off a lot of games lately). Other than that, my journal has the occasional random thought on larger industry trends, or a quick sort, like a toplist or the latest tier-making meme I saw. It’s interesting to see how my tastes change over the years.