That's the thing, SR2 isn't GTA, it isn't even trying to be GTA. GTA IV in my opinion didn't redefine sandbox games, San Andreas redefined that. If GTA IV was San Andreas wit the same amount of things to do, customization with the new graphics and so on, then it'd be redefined.
Thing is, what SR2 says it offers, it actually delivers on it. The fact it isn't a GTA clone anymore and now GTA's goofy cousin (purposely) makes it shine more in my heart then any GTA game.