Slightly OT, but modern game Alien Swarm is now out and free along with it's SDK/tools etc, and looks like it could be a contender for a allowing someone to create a CE remake... or similar game.
Example video -
[ Show youtube player ]
Website - http://store.steampowered.com/app/630/
p.s. Dan M, unpublished work - http://danmalone.deviantart.com/gallery/#/d20v52y