That's where things start to get debatable.
Now you get into opinions. I mean, the developers goal to make it are different. Look at all the SR3 trailers/teasers/gameplay. It's all about fun, madness and more fun, whilst GTA IV tried to make a story in a city. No more random Monster trucks races, RC vehicle battles, just more realism.
I liked SR3 more just because I know when I put it in my pc I will have fun and can laugh and I can't say the same for GTA IV. For the first half of the story I felt more a messenger/delivery boy then a gangster/****** person.