OK I just tried MTA ("Stop playing with yourself",
http://mtasa.com/) again after a couple of years. For San Andreas it only has a race mode, and that gets old quite fast, but it has some different modes from racing, like cars/robbers, dogfights and so on. And a really cool scripting engine. But no FFA deathmatch yet :-( It looked quite bugfree so far though.
Edit: Ok back from some more time with this. The multiplayer community sure grew a lot since I last tried it. THere's a ton of roleplaying modes and stuff, for mods other than MTA. Some of them seem really complicated and quite intriguing, but I just don't have the time to put myself into them :-\ You start off with some basic character and should try to earn money by driving people aroudn in taxi and so on, buy weapons, get a job as police man, pull people over, jail them bla bla bla...
I spawned in one of the really remote small villages, and there was no car around, so I called for a taxi. AFter awhile someone came with a taxi, and first thing asked me for money to pay the petrol bill. Then we went to the gas station and filled her up... then before paying I "had" to leave the server for awhile. Not sure how that works out. ;-D I guess next time I log on there I'm a wanted, seeing as you can put money on people's heads, and then people hunt them down.