I'm a big Marathon fan - or at least I was.
Marathon 1 and Marathon 2 (Durandal) were both great.
I'm developing mixed feelings about Infinity - the game play doesn't feel as fluid or as robust to me. I'm in the process of developing my own tribute site - check it out - comments/feedback always welcome.
I love the finer points of Marathon, to be it's almost a philosophy, not merely a game.
If anyone can help me with Infinity, Electric Sheep 3 - that would be great. The spoiler guide doesn't help me at all - I'm reading it, but find it doesn't correspond to my game.