For now I've decided that I'd rather be playing the game than writing a review, but I'll talk about what I can.
On foot
Walking and running ad sprinting. Those are the three modes you have. Without hitting any buttons and just moving the control stick, it's walking, and it's mindnumbingly slow. It's nice in the sense that you can realistically blend in with normal people becausse you're just as slow as them, but I'd still prefer how previous games were set up. Holding A lets you run, and tapping A is sprinting. Now, there's another cosmetic problem with the walking/running. Whenever you change direction Niko does this wierd lean to the side you're turning. I mean it looks more like he is walking on an angle, and it's creepy looking.
I haven't sene much combat being only two and a half hours in, and not going around just killing people, but when I was in combat, it seemed very sluggish. When I'd punch or shoot it seemed like there was a lot more time in between each punch and shot of the gun. I don't think that's a problem, the other games everything seemed unrealistically fast. I'll have to get into more combat for a better opinion, but Niko's sluggishness may be due to another issue I wanted to bring up.
Niko is fat. He isn't like, extremely obese or anything, but it looks like he has a bit of a belly. Or a lot of a belly really. Maybe it's just his clothes, because GTA games never really could make jacket look not fat.
Driving
Driving is different now, it's more realistic than previous games and the cars don't handle as easily. A nice feature I noticed was when I got into an old beat up car, Niko has trouble starting it, and when it is going down the road it will let out some smoke from the tailpipe and make a stereotypical car backfiring sound.
Misc.
Dating seems to be revamped, and I went on one date that I think was through the story, but I'm not sure. As they said they wanted to blur the lines between story missions and side missions, and they actually did a pretty good job of that, because side mission type things will actually call you on your cell phone, and seem to have an idea of the story and don't seem out of place.
I went on the internet for a little bit, but I didn't see much, I think I'll have to wait until I find out stuff online like secrets or something (read: porn), but I think it's a cool novelty that I might come back and visit later, like watching T.V.
Hookers a a little different. I only tried so I could give a better review though, and in no way rely on this gameplay feature to get me off. So, the hookers actually move in your car now, and you can choose between three priced jobs, $20, $50, and $70. My character was a chep bum, so got the $20 special, which turned out to be a clothed HJ. So, all you see is a hooker's hand going up and down over Niko's pants. I don't even want to think how crazy it will get at the higher prices.
I'm going to go play the game some more, I'll post more later today.