There are already tons of useful reviews on this awesome game, so I'll just make this a quick note for mac users: having a mac can be tough on gamers, as hardly any worthwhile games are released for it, and although Steam is great, it's not a lot of help either. The apple store however has a surprising amount of sweet games, San Andreas (as well as Vice City and GTA III) being one of them. It's only $15, no glitches, runs like it should, and it's much easier to access than if you had bought it on Steam anyways (just click on the icon in your applications bar). So if you were worried about a San Andreas port on to mac, don't be, it's still as great as ever.
That's all I need to say, but the minimum length for a review is apparently 800 characters so i'll mention the ambient sound in this game can be kind of lacking (when you're walking around in the streets of downtown you would expect an onslaught of traffic sounds and noises, but if you're on foot it can be dead quiet unless you make obvious sound effects like gunshots). It's been years since I've played San Andreas on anything else so i'm not sure if this is a result of it being on mac or if it's always been like that, and it just sounds inferior when compared to GTA IV or something. It was the only thing I potentially found fault with though. Enjoy!