I have to disagree myself. I found that huge lack of cohesiveness really dragged the game down the farther you got into it, especially since each successive area of the game had less to do and was just kind of there for the sake of being there. Things were fine when you were in Los Santos, but it was just downhill from there to the point where by the time I reached the third city I couldn't even stand the game anymore I was so bored.
And I will agree with ranking GTA3 above Vice City and San Andreas simply on impact alone. That game pretty much changed the face of gaming.