Just the right game for ambitious and greedy people!
You also have skills you can upgrade. These are "Fighting", "Shooting", "Health", "Speed" and "Street Smarts". Each one makes you better in a certain area. Fighting allows you to do more damage with your hands and extort faster; Shooting makes you aim more precisely and faster; Health increases your HP and resistance; Speed makes you sprint longer, move and attack faster and conceal/reaload your weapon faste and Street Smarts gives you a series of things such as heat and vendetta reduction.
The game's "experience point" is the "respect". You can gain respect by completing missions, taking over businesses, getting unique execution styles - this is one nice thing in the game; you can kill people in 22 different ways -, etc. Respect is what makes you go up levels. Each level you go up gives you one point to spend on the upgrade of one of your skills (maximum of 10 per skill). The higher level you are the easier it is to extort bussines owners.
Extortion is the way you take over other familie's bussinesses. You must extort a bussiness owner in order to take over his bussiness. Sometimes he might not want to cooperate so you have to either hit him or his "shop". There are four kinds of bussiness: Front bussiness (such as bakeries, hotels, etc), Rackets (brodels, gambling places, etc), Wharehouses and Transportation Hubs. Each one these gives you a weekly contribution in cash which you will use to bribe cops, pay doctors to heal you, buy safehouses and weapons.
This is basicaly the gameplay style that makes the game what it is. As you can't interact the way you want with everything it's not perfect but its pretty good.
About the system aspects Graphics and Sound aren't really good. The game appereance is as good as a modern game has to be but not any thing better than that. Enviroments are pretty repetitive, buildings inside aren't unique at all, not even the families houses. They're all the same according to their type. Speaking of repetitive things, NPCs are basically all "clone war" styles with some variations - same about cars, there are few types of them and they only change in color - the unique ones are the main charcters (Sonny, Don Coreleone, Clemenza, other familes bossess...) and your character. This is one very cool thing: you can change your character in evey single detail - from rinkles and scars to eyebrows, mouths, hair eyes color and etc. You can also change his cloth at any time and there are lots of variations of them. Besides these exceptions, developers could have given more attention to the variation of NPCs and building interiors.
One problem the game has is that you might get a bored with it after playing for a couple of times as things you have to do will be always the same. Think about this before buying this game, it is very important so you don't think it was a bad idea after you bought.
Considering all that, I think the game is really good and it manages to get quite close to the film story.