Mentlegen, I think you have all missed off the BEST FPS game of ALL time that there ever has been or ever will be.
Tom Clancy's Rainbow Six Rogue Spear.
you control 4 seperate squads, whom you hand pick from about 150 seperate people, each with their own talents and weknesses. You then pick each individual persons armour and weaponry (16 people in total)
you set each squad of 4 a route and timings to achieve
you can swap between the most senior and alive member of each of the 4 teams
if 1 bloke is killed, deal with it and play as someone else, it doesn't end there.
Doesn't run on Vista or later - you can pick it up for like £2 in CEX or the likes, I would really love to know if it runs on XP (failing that I'm building a windows 2000 Gaming rig)