First of all, RICKY GERVAIS IS FUCKING IN GTAIV HELL YES.
Next on the agenda:
I was really shocked by how the game managed to change since San Andreas. I'm only a few hours in, and it really feals like Niko was really trying to get away from a lifestyle of crime by coming to Liberty City, only to be thrown right back into the mix. The two girls you meet right off the bat aren't whorish at all, which is unusual. Hell, I might go on to say that this game's story might actually be the first serious crime drama game. Sure, the parody GTA aspects are still there, but I was really taken aback by how serious the game managed to be in comparison to the other games in the series.
The other thing that I was really struck by was how diverse the game population was. On the first dating mission, I ran into black people, Russians speaking about the homeland, and typical white assholes. The development team did an overall amazing job at replicating how diverse the population of a city like New York is.
I'm at work now, and I've only played for three hours (most of that time watching the TV, which is hilarious, I rofled at the Republican Space Rangers) but I can already tell that this is going to be my favorite game in the series. Especially now that I feel like my character is at least trying to develop some morals, at least at the beginning. It definitely deserves the tens that reviewers are giving it.
Edit: StrikerObi, amen to that, I'm amazed at how lost I am so soon into the game. Rockstar wins yet again with the GPS and the city design. I'm sure it's not easy to find your way around New York either.