This is with no doubt the best game in the whole GTA series. For a 2004 game, it beats the most recent ones.
Don't judge me when I say this is the best game in the GTA series, I've played them all (except GTA 1 and VC Stories). Even IV, this game is amazing but still it doesn't come close to San Andreas's greatness. Just take a look at it: the biggest map in GTA history, excellent storyline, amazing world to explore. The weapons, cities, mini-games, buildings, features, characters... I can't find any flaws, seriously.
I also like the settings, the 90's San Andreas, but at the same time it seems so modern. I know GTA V is coming soon and it'll be in San Andreas, or at least Los Santos, but it'll take a few time to make me believe it's better then GTA: SA.
In fact, I think the whole GTA III Era (GTA III to GTA VC Stories) is better then GTA IV Era (GTA IV to TBOGT), this, however, is my preference for 'oldschool modern' games, which I describe in my profile.