Some rules:
1- On wave 6 the madnes begin, you can hurt NPC`s and others human players
2- At wave 6 also the spawning boxes begin to spawn weapons of mass destruction (area weapons).
3- Theres a lot of weapons around the first map (melee ones), maybe hiden, you may take attention to messages an green lights
4- When NPC dies normally drops weapon or ammunitions
5- On wave 10 normally executes order 66 and launch a nuke attack, you have about 2 minutes to find how to escape.
6- When you escape the next map is enabled to play un single player mode, on multiplayer all maps always enabled but the escape dont allow you to go to end of the game.
7- Yes hidden somewhere is a end map..... and only you can reach it playing single player game.