The announcement that Alien Swarm was being resurrected, patched and then put onto Steam for free brought back some nostalgia to many players, but now it appears someone is pointing out that some simple console commands can change the top down shooter into an FPS for more atmospheric and intense gaming.
Topdown, RTS and MMO type gamers aren't really into FPS's, but this does make the game more enjoyable for FPS gamers to try out.
In a running game of Alien Swarm simply go to Options > Keyboard > Enable developer console. Then hit ` (to the left of 1) and type:
close console and play FPS style.