Pathways is a little too... I hate to say something like "archaic", but while I've tried to play it in the past I've never gotten very far. (I believe I made it to Lock & Load.) I have read over the walkthroughs and conversation texts, though.
Actually the Marathon Story Page is the primary reason I bought the games. It looked like such an interesting storyline I had to work through it for myself. I've read and re-read the terminal texts many times over the years.
The link to Siege of Nor'Korh you provided didn't seem willing to unzip properly. I eventually found an alternate link via moddb that seemed to work all right. Haven't yet decided if I want to play the various scenarios in chronological order or some kind of random-draw.
Abuse I've played heavily in the past, and Myth is one of the few RTS-style games I can stand to play at all. (The other being Irrational's excellent Freedom Force duology.) I'd be more likely to replay the original campaign under the Myth 2 engine as The Fallen Levels.
Still waffling on whether I want to replay that as part of my Tour of Shooty build-up to Destiny, but given that I'm already making a flimsy excuse to replay Oni for sure, I might at least install it and lose hideously on the third map.