as a fellow gmod fan i would like to inform you of a fun map/mod galled onslaught, if you haven't head of it it's a large opem map where you build your defences them press a button and the enemies start spawning, first just hordes of easy zombies, them faster zombies, then combine and antlions etc getting harder as time passes. works best over highspeed lan with powerful pc's as the huge number of npc's put a lot of strain on the networks and computer systems. it is playable with 2-3 people over a broadband connection but gets laggy as the enemies build up.
(google onslaught and garry's mod together)
ps i'm downloading the vid now
edit: what media codec have you used?