Wow that was a long post and very fulfilling to read. Nice.
Now I guess I can't really state a full opinion because I haven't played the other two, but I am deeply in love with M1. If you go to the link in my profile I have my own little fanfic, which seems like just a story but is really just an outlet for my obsession with the game. Durandal is, in my opinion, the best character ever created for a computer or video game. The originality of M1 is so obvious even today, despite the fact that there are so many games out now that are very similar to it. I also think that without the background and depth of Marathon, Bungie wouldn't have a leg to stand on creating Halo. I've gotten into Halo, but mainly it just reminds me of the game of Marathon that I still haven't finished, so I get off and go play on the Mac downstairs.
I'm really confused about Tycho though. As far as I've seen, he really isn't mentioned very much except for Durandal's mention of him(which is garbled anyway) and his little rant on that terminal I couldn't get to. I remember hearing once that Tycho IS Durandal, but I guess that's not true. Is Tycho not rampant as well? He seems like it.
Anyway, I was a bit surprised to hear that Mi is not as good, but I'll end up playing M2 and Mi anyway, just so I can have some closure. I'll also try Aleph One, but I'm still not sure how to set it up.
Thanks for the input and info!
