The main problem I had with GTA4 (though I did enjoy it thoroughly, nonetheless) was the complete lack of any non-story-related activities to partake in during the main game. Yea, you could do the whole "dating" thing (which got old after a while)......or get into trouble with the law (which was more fun than it had ever been in the series....but not enough to make it an all-the-time activity), but outside of that there really wasn't much to do with the game's amazing virtual city. The raw material for gameplay was there, it was just underutilized. I also think this is why so many fans coming from their San Andreas fandom gave the game a thumbs down. San Andreas just had tons of things to do that fell outside of the main narrative, and GTA4 just didn't deliver that same level of urban interaction.
I'll give Rockstar the benefit of the doubt, though, being as this was the franchise's first foray into the current gen. The game engine itself is just fantastic, and I'm sure alot of dev time went just into realizing such a vast, detailed environment. GTA3 now looks equally dumbed down compared to its Vice City and San Andreas successors, so the odds are GTA5 will fair much better in the extracurricular activities department than 4 did. I'm also hoping that North takes some cues from the San Diego team...Red Dead Redemption was a much more engaging game than GTA4, despite the handicap of being set back in the early 1900's. There's no reason why a game set in a modern day urban sprawl shouldn't offer vastly more gameplay fodder than one set in the ole' West.