I was seriously just playing this on Steam. Like, I literally closed the GTA:SA window, opened my browser, came to GC and saw this thread. I still think it's more fun than any of the other games in the series. GTAIV was fun for a while, and definitely has a better storyline, but the driving mechanics are frustrating (too realistic) which makes it less entertaining to me. Also, I loved the huge map in San Andreas, especially the rural areas like the desert and dirtbiking paths in the forest. One thing I didn't really like about the game was the radio stations, which is why I'm so glad the PC version allows you to use mp3s. Then again, I've never been a big fan of the radio station tracklists in any GTA game. The reggae station in IV is the only one I've ever really liked (there might have been one in VC too but I haven't played that game in forever).
I love GTA SA for all the things you could do in that game. Fly airplanes, a lot of Easter eggs, funny shit, etc...
The radio stations for me was the one of the best aspects of the game I dunno, had a good feel to it for me