People who create extra accounts for this kind of thing are sad, sad people who deserve only pity. Besides, this is for fun, not for SRS BSNS. Losing is fun, and it's not like people on the losing team will just keep getting shafted, just that the plot will go a little differently. That, and I think I can apply some common sense where sheer numbers of people completing missions are concerned (re diminishing returns, or something similar).
Difficulty isn't going to be absurd for most stuff. A reasonable newbie to each game (but still a gamer in general) is likely to complete, oh, easily half the missions although some will be a big challenge to finish. There'll be more hardcore ones too, sure, but I'm aiming for "it's fun having varied experiences I wouldn't otherwise have, and watching the plot evolve around me while I get occasional shiny medals and ribbons". It's not "I must prove my internet-tough-guy value by winning everything forever". Friendly competition; I'm sure you people are capable of it, and the world won't end if some guy on the other team is a douchebag.
As for multiple teams, are you trying to kill me? Writing plots and fun missions for two teams is going to be time-consuming enough, considering that they aren't precisely symmetrical. Besides, it's still casual enough that people can hop in or out of the game at any time without wrecking their team. "Oh god I have to play this week or my team captain is going to be angry" is, well, not what I'm after. That, and only having two teams means that I can write a bit ahead of time, and it's good proof against people who drop out and leave the plot hanging.
MechWarrior 4 is here:
http://www.mektek.net/projects/mw4/download.html It's kind of weird, but that program is a neat (official!) matchmaking client that includes a torrent-thing that downloads the actual game itself. You tell it to install the game, then it'll want to grab a patch, and poof it works. It's like a gig and a half, but it's a solid game on its own.
Doom: I'm personally going to do my Doom stuff in either ZDoom or Chocolate Doom (which is a source port with, like, zero extra features whatsoever except that it works well in modern OSes). I'll start it out with Doom 1.9 Shareware. Snag
ZDoom or
Choclate Doom and the
Doom 1.9 Shareware WAD (bottom link). You can run it with the full version of Doom 1 or 2 as well, but the shareware makes it a free game. <3
Sid Meier's Alpha Centauri: The free demo will NOT work for this, sadly. But you can still
play it! Even if you don't get it for this, you might still have fun with it.
X-Com, I'm not even going to try to screw with the demo version. But hey, the full version is five bucks on Steam and Direct2Drive and probably other places. Then again, if you like games like X-Com you probably already own it...but who knows? (For the record again, X-Com missions
if I can get them to work will be battlescape only, no geoscape.)
SpaceChem: The
demo won't let me make custom levels. But again, see if you like it, it might be your thing.