Bungie's Halo 0.1
I've been meaning to find out if this game is worth playing, is it?
Which one? Halo or Marathon?
Marathon was Bungie's first good game. It's a Doom-like game for the Mac only. Since PC users had Doom, Mac needed their own big FPS. And in quite a few ways, the Marathon trilogy is superior to Doom. The graphics are slightly better, the storyline's more complex. There's a flamethrower and civies you can light on fire.
After Marathon, Bungie made a D&D-based RTS pair, Myth and Myth 2, both also on Mac only. But both are really really good, with realistic terrain and specialized units. You don't build anything in Myth, you start with an army and you have to keep them alive. I haven't seen either online.

Then came Oni *bleh* and Halo 1-2.
If there were three Mac-only games I would sell my soul to play, it would be Marathon, Myth, and Escape Velocity. Well, I got my first wish.