You tried to connect to your own server? You need to use 127.0.0.1 if you want to do that. Also make sure that you have started a server and the correct ports have been forwarded before your friends try and join.
You can use http://www.whatismyip.com to find out your ip.
They havent added peds because of the lag it would cause. They would be just like other people ingame, causing more lag then there already is.
The monsters being mutations and not demons really pissed me off. It cant be a DOOM movie without a reference to Hell. At first it wasnt supposed to take place on Mars, not sure if the changed their mind or not.
So the game basically crashes? If thats what you're talking about its normal. Since this game is still in beta form it will crash everyone once in a while.