The multiplayer community on Gmod is still thousands of servers which are achieving around 10/20 players average, there are large communties with hundreds of active players and many smaller communities which manage lower yet still consistant numbers. Using the various mods, the servers create mod packs for the type of gameplay they want. There are Warhammer 40k servers, Star wars role play servers and many more. These servers are usually very welcoming to new players and even if you know very little about the server genre, you can still have fun as there are servers that are serious, semi-serious and more fun servers with serious servers being hardcore and very strict.