One of the sweetest series I know. Reminiscent of other supernatural adventure series like Inuyasha, but instead of fights, Natsume makes friends! (One of my favorite running gags is the way "fights" tend to be resolved in this series.)
I think this series really captures that feeling of being lonely and not knowing how to understand or interact with others. As an only child, I felt a real kinship with Natsume when I first watched this. Because of the overall tone, even episodes that end happily always leave me with that bittersweet feeling, but in a good way.

It's pretty episodic. There is a very slow moving overarching plot scattered across this show's many seasons, though I think the first and second are definitively my favorites. Anyways, it's definitely a worthwhile watch.

Also, I want to give the soundtrack an honorable mention. I can't quite find anything else to say about it except that it's pretty memorable even after all of these years.