Most players tend to play Singleplayer or organized co-op against the AI. This is especially true for people who play with mods; the game has quite a selection of mods that change the game quite a bit, but multiplayer for those mods is, AFAIK, basically non-existent.
That said, the game does have a multiplayer community, though it is more small and dedicated. Since the way you play multiplayer is vastly different from the way you play singleplayer in this game, newbies have a lot to learn and the community isn't always patient enough to let them learn. If you want to play this game multiplayer, you better be ready to wade through DotA-level toxicity without the benefit of a large playerbase. Plus the game's multiplayer interface and infrastructure is roughly that of Warcraft 3 custom games'; server disconnects and desyncs are not uncommon.