In reference to the vanilla, no-DLC version of GTA IV, yeah, it fell out favor with me. The difference between GTA IV and San Andreas is like the Earth versus Mars. I kept finding cool details in IV but lacked the ability to interact with them. I'm talking about the empty golf driving range on the Lower West Side that you couldn't use. And then there were the three empty skate parks I found which I couldn't interact with, again without actual skateboarders in them. It's not like I wanted jetpacks; I just wanted some minor distractions other than just drunk driving and shooting pigeons.
I don't blame Rockstar entirely for the lack of activities though. I also blame the millions of customers who (probably) bought previous versions of GTA and just fucked around, entering cheat codes to get the chainsaw, and started butchering prostitutes. Screw the side missions, much less the actual main storyline, right? The only gamers I personally know who played San Andreas did just that, and perhaps Rockstar somehow found out, like though focus groups.
Then again, IV was such a huge graphical jump from San Andreas (not to mention a generational console change) that Rockstar probably didn't have time to do all the smaller, cool stuff. I'm glad they announced all of that for GTA V.