okay since i am a big coop-fan, here are some tips about hosting one:
-network-mode:
i usually host coops in p2p-mode and play on the same maschine cause that reduces the crahs-happyness of d3. for some odd reason coops in cs, cs/d crash more often. (its probably my uploadspeed i have only like 256k avaible)
-pps:
use at least 10 pakets per second, 12 is better. coop causes a lot of datatraffic and people will disconnect more often if lower then 10 pps is set.
-playernumbers:
coop can be played with max 4 players, if you host a cs/d server you can only play with 3 cause the dedi takes 1 slot.
-respawnrate:
when starting the game, you can set the respawnrate for powerups to a minimum of 10 seconds, even if you put in lower values, d3 will take 10 seconds. but coop is no fun with blues and a few concs, so after starting the game press f8 and type:
$setrespawntime 1
and you will have 1 second fast respawns. (only the player that started the coop can do that cause he is "server")
-levels:
descent3 retribution provides 17 levels for coop (1-15 and 2 secrets) my favourites are 12, 15 and 17, but most of the others are good too. some of the retri-levels will cause strange bugs during game, for example the powerup-respawn will stop after a while and you have to fight without supply
level 14 is an example for this.
there are a few custom sp-missions that allow coop like monument and some levels from solrazor (kyo).
mercenary can´t be used for coop, it works only with a little trick. and even then only a few levels of merc can be played in coop cause of the levelscripting (well you can play all but finish only a few). mission-critical items are missing if hosted in coop.
merc levels that work in coop: 1,2,4 and 6.
-playertips:
as player you should follow some rules:
1. dont use guidebot, let it out only if absolute nessecary. guidebot will pretty sure crash the coop. (i have seen server crashing even if some player switch on headlight)
2. remove your gam-hacks before you join, you will crash the server, you lamer
(j/k)
3. almost every retri-level has a few spots, if a player goes there the server will most likely crash. dont ask me why. an example would be the small corner in secret2 where the massdriver is, or in level 15 the place with the bomb-game. there is a small hidden cave with a flametrooper, dont go there.
4. listen to the gamehoster and do what he says, coop is not "lone ranger rushes through the game and ruins it for the others" its name is cooperative for a reason.
some of the levels have scripting-bugs like closing forcefields and doors. if the gamehoster says: "dont go in the room" then gdamit dont go in there
for example retri level 6, 12 and 15. nothing worse then fighting 2 hours in level 15 to face the boss, and then one player passes the last energy-center, the forcefield will close and all other players are locked out.
listen to the gamehoster!!! hehe
however, a good coop with the right players can give you tons of fun, its worth a try. i have played most retrilevels probably 15-20 times or even more in coop and still find something new sometimes. the games are allways going different directions based on how the players move on and thx to the good robot-ai in d3.
Dig out.
There are so few coop games around, none most of the time... I was having a great time playing then all of a sudden the robots didnt blow up any more and you were frozen PID. I forgot your name, was it PID? I should have taken a screenshot.
I just launched the game and saw the option. I must be going blind.