I'm not sure about Myth III, from what I understand, Bungie handed it to someone else to develop.
I played Bungie's first two releases of Myth; Myth: The Fallen Lords, and Myth 2: Soulblighter, and loved it! Great for multiplayer deathmatch, co-op, or simply single player. It's also somewhat streamlined, so you get a "Warcraft III" style game (and Blizzard based many aspects of Warcraft III on Myth intentionally) that'll run on near any Pentium class system.
You might want to read some of the personal reviews at amazon or gamespot. I heard some other company made it and they had to rush it as all the programmers were going to be fired when it was done. And overall, the user reviews (not the pro ones) were quite bad! And the game has no support from the maker from what I've heard - I guess for obvious reasons.
I heard such good things about Myth II I had to pick up a cheap copy on ebay.
[This message has been edited by Chiles4 (edited 03-28-2002).]