I'm back, and sure enough, delving into Obsidian turned an experiment with it into using more regularly.
Having come from Joplin, I can say that while Obsidian has a lot of cool features, Joplin is open-source, seems to support nearly all the same features (it also has plugins), etc. and the one thing I've heard people cite as a weakness is, to me, a strength (after a few weeks working with Obsidian):
With Obsidian, the markdown file has the same filename as the note's title-- there is no distinction, so you can not name a note with any characters that are forbidden in the file system. This broke tons of my note names when I important, and some just can't be fixed (how many notes do I have that are titled with a question?). Joplin mangles the markdown file's name, and stores the note's name as distinct from the filename, so the note names remain intact, irrespective of the filesystem. Joplin also stores the data in a straight directory structure, with no hierarchy, but inside your Joplin.. uhh.. vault-equivalent, there is one.
I think if I had known more about this topic (not just note-taking, but PKM in general), when I started using Joplin, I might never have switched. It seems most of the other features I thought were missing from Joplin are actually available if you go to look for them. It has several export options, too, if you wanted to take your data (remember-- open-source) to another program.
I will give Obsidian props for several things: thriving community, insane number of plugins, pretty UI, and seeming to sit well with the committed PKM crowd. I happen to like (but others would likely feel the opposite way) that you have to come up with your own synchronization arrangement, unless you want to pay for their service.
For joplin: mobile app works pretty well, supports natively several types of synchronization, and isn't just the desktop app crammed onto the device's screen. Joplin also seems to be much more stable as far as the editor goes-- both the markdown and WYSIWYG editors. Feels more solid-- a truck, not a sports car.