Well, being realistic can be good or bad in GTA series. I personally hate the phone option, you can't get it out anywhere and Niko puts it back in his pocket willingly quick. Cheating gets harder and harder in GTA series :D
Also, jumping out of a burning car is not an option anymore, since you'll be dragging across the floor more than the car you've left, putting a good chance that you'll end up next to it when it blows up.
Another one, things have been much more sensitive, a random action can return unexpected consequences.
Also, Niko does not have an option between dead slow walking and sprinting at top speed, which makes him tired shortly. The clothing and weaponarizing options were decreased as well.
In short, GTA IV gains from being "realistic" at some points, and good graphics of course (but i find it less efficient using resources). This makes me think the following games will have more options on things. Some time, we'll play a GTA game like San Andreas with better graphics. We'll see what happens then.