"Marathon" had been out for quite a while when "Doom II" was ported to the Mac. "Marathon", with its multiple degrees of freedom for aiming and movement in addition to mouse-look, made "Doom II" feel quite old. I think that "Marathon" may have been the first game in which you could use rocket jump, grenade jump, and mouselook, though I could be wrong. Actually one thing that I'm sure that "Marathon" did first (at least in an F.P.S.) was have a minor branch in the story which made you do a different mission depending on how many B.O.Bs were killed in the mission in which you were to protect them. Interestingly enough there was an O2 gauge in addition to the Health gauge and that was utilized in that mission where you had to power up the communications dish, man was that a pain—then you were told that the message wouldn't reach Earth for 99 years since you were about 99 light years away.
I remember using the physics editor to edit some of the weapons. Once I altered the punch so that it had a flash of light that lasted a couple of minutes, in essence a flashlight. Actually, I do remember one physics file that managed to allow you to use 2 Zeus Fusion pistols—although sometimes it would work just fine and other times it would crash the game.
Does anyone remember "Pathways Into Darkness"?