After spending well over 40+ hours in Liberty City I feel I have a very strong understanding of how the game is played. After played through as much of the game as I have you get to see the pattern of the game play. Liberty City may be one large open world where you can do what you want but the game does steer you in a specific direction if you play within the rules.

The game is called Grand Theft Auto for a reason; you will be stealing a lot of cars.  There are occasions you are given a car or you can use your cousin's car service but for the most part to get around town you need to steal cars.  This gives you a couple options: steal a parked car or car jack someone.  Really car jacking people in this game is supper easy because most people don't fight back.  As long as a cop doesn't see you jack someone's car you are also safe to drive off at your leisure.  Stealing a parked car may sound an alarm and possibly alert the police. 

There really is only one mode of transportation in Liberty City: car. You will spend more time driving around than any other activity in GTA4.  That's not bad considering there are 19 radio stations to listen to and some very bizarrely funny commercials and talk radio stations. Let’s just say no one is safe on the radio in Liberty City. There is a tree hugging liberal public radio station that pokes fun at the health care system and activist actors.  Then you have the conservative radio station that beats the drum of fear mongering and attacks the liberals.  Or you have the rock DJ that trashes corporate radio but uses commercials to pay for his yoga classes.  Really the smartest commentary of American culture in the game comes from listening to the radio.

Most missions require you to drive to some location, commit some crime, possibly shoot your way out of a bad situation then get the hell out of Dodge.   On occasion you have the car chase missions where you have to chase down some fools and kill them.  These are almost always bad people that needed to die so there is no guilt.  Really the car chases are a lot of fun but some of the cars really suck to drive. 

For the most part cops will chase you in GTA but depending on how many stars you've got will determine who long and how through they will chase you.  One star is easy to ditch with a couple quick turns.   Two stars aren’t that much more difficult.  Three stars gets interesting with helicopters and a lot of cops.  Four stars brands you a terrorist so everyone is after you but you can still escape. Finally five starts are probably impossible to escape since the whole city does on lock down and there is no place to hide.  If you shoot a cop it's an automatic three star situation and often you need to shoot some cops to get away on specific missions.

Other than those missions where you have to shoot cops, the game really leaves the moral choices up to you.  You can either let a guy go or you can kill him.  Or you can deal drugs for your friend or you can skip those missions.  You can also run around killing civilians or hookers or you can just ignore them.  You can drive drunk and most likely get the cops to chase you or you can catch a cab or call for a car.  All these options are for you to choose how you want to play the game.  The game does not steer you towards making bad choices but it does flaunt them in front of you.

Update - Not sure what happened to this post but I've removed all the junk that got in the original post.