I love the GTA series and I've had hours of fun playing them, but I really think the extremely high scores for San Andreas were not justified. To me, the gameplay additions weren't enough to offset some of the more serious flaws:
1. Graphics - I don't think I'm a graphics whore, but the character models and textures were not up to par for a game this late in the PS2's lifespan. Character animation was fine, but everything looked very blurry and primitive up close. Also, some of the lighting effects made it impossible to see what you were doing. I know they were going for a realistic and cinematic feel, but when headed due west at sunset, you often completely disappeared because of the contrast.
2. Character customization - The tattoos, haircuts, and clothes shopping was neat, but the load times for the different items were ridiculous. I don't understand why they couldn't have let you preview the items before having to go back and forth from the changing room to see what you looked like. It was just too time-consuming, and I ended up not bothering with it much at all. Even PS1 games have had better systems for this type of thing.
3. Aiming - This was a much more serious problem for me than the graphics or customization. No matter how much anybody says the aiming system was improved from the first two games, I had a lot of trouble locking on to targets accurately. I can't count the number of times I tried to lock on to someone and turned completely the opposite direction, or somehow managed to shoot straight into the air, resulting in my promptly getting killed
4. Repetitive / overly long missions - I guess all the games in the series have suffered from this, but it was frustrating to have to do a mission again and again if you failed it the first couple of times. A lot of the missions seemed to involve driving for several minutes to one location, or to have conditions for success that were just too demanding (trying to drive across town without damaging your car one bit, etc.). There were times I spent half an hour trying to complete one mission.
I really think that these flaws, in a game that didn't bear the GTA name, would have resulted in MUCH lower scores - probably in the low to mid 7's. Don't get me wrong, I had fun with the game, but I don't think it deserved high 9's and perfect scores. That's my take on it and I've tried to give my reasons as best I could. I'm interested to hear what anyone else thinks.