It may be two Grand Theft Auto generations and 11 years old, but GTA:San Andreas is still very much alive. Its two most popular multiplayer mods currently have a million or more active players between them - One Multi Theft Auto, had 616,000 players in July (up from just 33k in February 2010), while the other, SA-MP, oscillates between about 15,000 and 50,000 concurrent players. I went to talk to members of both mod communities to find out what keeps them playing.
These certinaly aren't numbers to be sneezed at. They put many of the biggest current PC games to shame. Even the massively-popular GTA 5, replete with a sprawling online mode of its own that consistently puts it in Steam's top 10 games by player count, fares no better than its ancestor. (To put a number on it, SteamSpy estimates over 1.2 million GTA 5 players in the past two weeks, with peak concurrent players consistentl around 50.000.)
There are lots and lots of options for roleplay across the two multiplayer mods, some narrow and focused like the prison and trucking servers and others broader and more ambitious and reliant upon a whole virtual society forming within the San Andreas world (or a custom map). MTA has even a server where you can get a job as an astronaut and fly to the moon to mine moon rock.