Top of the recommended gmod gamemodes.

1.DarkRP: Its a roleplay gamemode,its like your second life.you can mount your own role and play any character you want... a police,a chef,a criminal,etc...
2.TTT: There are two teams: The traitor and the survivors. The survivors objective its find who is the traitor,but obviously will kill some innocent people. The traitor it's obvious,kill all the survivors.
3.Murder: 3 teams: Murder,survivors and sheriff. The murder objective its kill all the survivors and sheriff. Sheriffs objective it's to kill the murder with his revolver. And the survivors objective e it's to evade the murder,they can even pickup the sheriff revolver to kill the murder.